World Tennis Number (WTN) algorithm changes coming

I saw a mention of an email sent out from World Tennis Number about algorithm changes, but I hadn't seen it, so I went and visited their site and in the news section is a story on World Tennis Number Algorithm Enhancements 2026.

Many of you probably don't follow your WTN, as for USTA League players it is largely meaningless other than it being a rating you can track.  But it doesn't directly relate to your NTRP rating or dynamic rating, nor is it used for anything related to leagues.  I'm a ratings geek so I do follow mine, and if you follow yours too I'd be interested in hearing from you or leaving a comment about your experience with it.

If you have followed along with WTN news, you will be aware that this isn't the first time there have been changes.  At a minimum there were changes in 2024 to try to have WTN ratings represent a player's ability more quickly, and widespread adjustments in 2023 to redistribute players along the 40:1 scale.  You can see all my WTN posts here.

So, this isn't the first change, what is changing now?  A quote from the article is the changes will "improve rating accuracy, reflect real match performance, and support player development at all levels of the game".  Here are some highlights from the news article above:

• Changes go into effect for the calculations on August 12th
• There will be a rolling 3-year rating window where older results gradually drop out of the calculations
• The algorithm will use game-level scores, not just who won the set
• Ratings may be "gently adjusted" based on age, time since last match, and "typical development patterns"

The biggest news to me is the move from only looking at who won a set to factoring in the score of the set.

Up to this point, if you won 7-6,7-6 the WTN algorithm would treat that the same as if you won 6-0,6-0.  In my opinion, there were pros and cons to this.

On one hand, winning sets, and the match, is what matters, how you do it doesn't really matter, so if someone had a track record of winning close matches, they should be rewarded for that.  The algorithm was also a little simpler and easier to understand (or reverse engineer?) and less prone to being gamed by someone managing scores.  If someone played enough and against stronger and weaker players and accumulated wins and losses, their rating would settle it and represent their level.

On the other hand, ignoring the score is ignoring valuable data.  Clearly, winning 6-0 is different than 7-6 and ignoring that seems foolhardy.  If someone plays a strong opponent and keeps it close, they don't get rewarded for that, and if that player happened to always play strong players and lose, their rating could perhaps inappropriately keep getting worse.  Using the score in a set would allow for rewarding a player for keeping it close.  And if someone didn't play a lot of matches, their rating could inappropriately go up or down based on very few matches with limited data, and using the game score would fill in some gaps.

Now, in the algorithm to date, winning sets in a given match was not treated equally, but how much it helped your rating depended on your rating and the rating of your opponent.  Win a set against a much weaker opponent and your rating would improve very little.  Win a set against a stronger opponent and that would raise your rating a lot.  So some of the cons were mitigated a bit and there would be some limit on what a player's rating could get to by only ever playing weaker players and winning.

So, is this change a good thing?  I think so, but it will depend on exactly how it is implemented.  I don't know of anyone trying to game their WTN, but using game scores opens the door to that.  But if that is a rare occurrence, WTN ratings may become a little more representative of a player's ability.

What do you think?

A bit more on the recent WTN algorithm change / adjustment

I wrote a few days ago about the recent significant change to WTN ratings that the USTA sent a notice out about, and many players saw their WTN get larger (worse) overnight, some in the high single digits, but others went up 10 or more.

I don't have any detailed analysis yet, but do have a few more observations.

The USTA published an FAQ about the changes that is worth a quick read, but it had a few interesting explanations.

First, some insight into why the change was made:

These enhancements to the ITF WTN algorithm will reposition cohorts of players on the current scale of 40-1 and ensure that players from all over the world are more accurately aligned, particularly with regard to different age groups. While ratings are likely to be adjusted, players will likely see movement relative to their age group.

So, they seem to have concluded that different age groups of players were rated correctly relative to each other.

Going on, they get more specific:

Adult players aged between 19-29 should expect only minor changes to their ITF World Tennis Number. Larger changes begin to occur for players over 30 years old that regularly play against players of a similar age. Adult players over 30 will see their numbers move down the scale (towards 40), this is to create some balance with Junior players and to ensure full use of the 1-40 scale.

This is consistent with my anecdotal observations that USTA League players around me, for the most part age 30+, have seen their WTN get larger and closer to 40.  I haven't looked at any juniors, but believe their statement to be true.

And from what I see, USTA League players are by and large are all in the mid-20s and higher.  I see 4.5 and 4.0 men in the mid-20s and the majority of league players are at 3.0-4.0, so that means the majority of league players are being squeezed into the 25-40 range.  That is quite a bit less granularity than we had before (15-40) so we will see how that works out.

Regarding juniors, the FAQ states:

Junior players aged 10 and under will most likely experience a movement down the scale, (towards 40) with players who are aged 17 and 18 moving up the scale (towards 1). The player ratings are now more of an accurate reflection of age, with a general incremental increase expected from aged 10 upwards.

I've also heard from players in the UK and US looking at comparisons with players in Europe that prior to this change, there seemed to be a disconnect in that what appeared to be similarly skilled players from Europe and the US had significantly different WTN ratings, those in the US having lower numbers, so this adjustment seems to have addressed that, at least somewhat.

All of this highlights the challenge of a single algorithm that tries to put all tennis players in the world on the same scale.  Whether it is age groups or countries or other geographic grouping, you will inevitably have islands, or cohorts as the FAQ says, that all play each other, but have little to no play with other islands or cohorts.  When this happens, the algorithm has very little data to go on to reasonably ensure players from those different groups are appropriately rated relative to each other.

This is probably the biggest challenge for the WTN, and as such one would have hoped a lot of effort would have gone into reviewing this and getting it right prior to launch.  If adult USTA League players were rated in the teens and similar recreational players from Europe were in the 20s, that should have been one of the first things that was reviewed and stuck out.  Similarly if all juniors regardless of age were clumped together, or juniors relative to adults seemed off, this could have been observed far earlier and address before WTN was launched.

There are ways an algorithm can address this, notably by looking at the matches that are played between the islands of players, and giving them more weight in determining the relative ratings for the group of players they represent.

This is effectively what the USTA does with NTRP, using the matches from Nationals to "connect" the different sections, and have those results and how well a section did trickle down to players from the section.  If a section does very well at Nationals, that means relatively speaking the players from that section at that level were rated too low relative to other sections, so player's ratings may go up and more bump ups will occur.  It can go the other way too, and I've pointed out the effect of this in many of my year-end rating analysis'.

I'm guessing the WTN doesn't inherently do this as part of the algorithm, as it seemingly required this significant adjustment to compensate for what they were observing.  Hopefully they still applied the principals of leveling across cohorts and it wasn't entirely manual.

Another challenge the WTN has, and one that doesn't seem to have been addressed yet and wasn't mentioned in the FAQ is gender neutrality.  The algorithm claims to be gender neutral, i.e. just like a WTN 25 male should have a competitive match with another WTN 25 male, either should also have a competitive match with a WTN 25 female.

It is generally accepted that NTRP which is not gender neutral has about a one level (0.5 NTRP) difference between the genders, e.g. a 3.5 male and 4.0 female will be similarly skilled, but looking at WTN ratings one will regularly see men and women of the same NTRP level with similar WTN ratings or even the women having lower (better) WTN ratings.  Similarly, you will see men with higher (better) NTRP levels having higher (worse) WTN ratings.

This means WTN really can't be used to get cross-gender competitive matches today.  And WTN is really handcuffed now when it gets to trying to solve this as it now has to fit both men and women into this compressed 25-40 range I noted above.

For example, looking at men's WTN ratings, leaving room for the 2.5 and 3.0 women to have higher WTN ratings than 3.0 men, and leaving some room for complete beginners not even playing matches yet, the WTN range all recreational men have to fit into is more like 25-35 at best, and perhaps even less.

The change made to WTN may very well make it better than before.  But the challenges of truly being a world tennis number are still there.  It will be interesting to see how it continues to mature.

WTN lookup now available on ITF's site with additional features

After many e-mails from the USTA about it, the ITF World Tennis Number (WTN) was rolled out on usta.com about a month ago, and today I got an e-mail that it is now available on the ITF's worldtennisnumber.com site.

The player search page has a footnote that it is currently only showing USTA players.  I'm not sure why this is as the LTA launched WTN about six months ago so you'd think those players could be available too, but at least for now they aren't.

The search is interesting in that it seemingly only lets you search by surname (last name) or a tennis ID.  The type ahead last name search isn't terribly useful as there are often many players with the same last name and the player you are looking for may not be in the four they show.  So you have to finish your search and get the full list which can then be filtered by gender, country, and singles or doubles WTN.  This is an interesting way to search as if you knew the WTN, you probably wouldn't be looking!

But you can put in a range and narrow it down and presumably find who you are after, at which point you can click on them and get a page that is similarly branded to what the USTA sites shows, but with more detail!  The same animated WTN widget is there with singles and doubles WTN and Game zONe numbers, but on the overview page you additionally get:

• Match activity with a count of unique singles opponents, average singles interval, and average doubles interval
• Rating range that can show the range for singles and doubles for all time or the past year
• A chart of "player tournament matches" showing the count of wins and losses by month, filterable by singles or doubles, although it does appear to include USTA League matches too, not just tournaments
• A results summary with the win-loss record which can be filtered by singles/doubles/both and different time periods

Based on the results summary, it does appear it includes matches, for me at least, that were played in 2016, so I'm guessing that is roughly when the data starts the USTA provided to the ITF, which is consistent with what we've seen/heard elsewhere.  In fact, one can go to the Results tab and there, the date filter goes back to July 1st, 2016 so that appears to be the start date for WTN.

The Results tab is also where you can see more details with the specific matches including the players, their WTN, and the score.  They are actually grouped by event/league which is kind of nice, but oddly had a a stray match that wasn't in the right league.  The WTN shown does seem to be the WTN at the time of the match, so you can see how it changes.

Then there is a Head to Head tab where you can search for another player and see a head to head comparison of WTN ratings and if they've played, the records.  It seems to only do this for singles matches though so you can't find your stats with a partner or against a doubles opponent.  It will also show competitors in common which may be useful if you are scouting a future opponent.

All in all it is a nice presentation and it does provide more information than the USTA's site does and adds some additional useful context to help understand more about your WTN and playing history.

What the USTA could learn from the ITF - How to break ties in round-robin play!

The ITF Billie Jean King Cup, the event that used to be Fed Cup, is taking place this week in Prague.  It is a competition between countries

In the past, Fed Cup was played over three weekends throughout the year with four pairs of teams facing off one weekend early in the year with one of the countries being the host, the the winners advance to the semis two pairs play with one country being the host, and the winners then play the final near the end of the year with one of the countries being the host.  The format for each tie was two singles matches on day 1, then reverse singles on day 2 followed by a double match to potentially determine the winner if the singles matches split 2-2.

In its new form, there are 12 countries that compete, and the whole competition is played over the course of one week all in one location.  Instead of having an elimination bracket, the 12 teams are split into four groups of three countries each where each country plays two round-robin ties against the other two teams in their group.  Each tie is two singles and one doubles match.  The winners of each group advance to the semis where an elimination draw is then played.

For those that follow USTA League, this format probably sounds familiar, as Nationals uses round-robin play to determine four teams to advance to the semis to play an elimination draw.  One of the issues I've identified in the past is how the USTA determines the standings if there are ties on wins/losses, so naturally I wanted to see how the ITF did this for a group based format to see if similar issues existed.

With round-robin formats, it is possible, and often happens, for teams to tie on win/loss record.  When this happens, the event determines how to break the tie using other finer-grained criteria than wins and losses.  In the case of the USTA, they use:

• Individual match/court record
• Head to head
• Sets lost
• Games lost

What the ITF uses is:

• Head-to-head
• Percent of matches won
• Percent of sets won
• Percent of games won

The criteria look similar, but there are some key differences.

First, the ITF places head-to-head ahead of the other criteria.  One can debate which approach is the best, but there are some that think the USTA should do the same.

Second, individual match/court record and percent of matches won is effectively the same, so the next difference is sets lost vs percent of sets won.  These may sound similar but are in fact different, and the ITF gets this right while using sets lost is one of the flaws in the USTA's tie-breakers.  Using just sets lost ignore actually winning sets, while percent of sets won includes the won and lost sets and is more comprehensive and equitable.

Third, if teams do happen to still be tied, the USTA uses games lost while the ITF again gets it right and uses percent of games won.  Using just games lost is a huge flaw in the USTA's approach as this criteria rewards losing a set 6-0 (six games lost) over losing a set 7-6 (seven games lost) which is clearly inequitable, but the USTA has stuck with their criteria despite feedback and a regulation change proposal to fix it.

Before you say, it isn't a big deal, the tie-breakers never go this far or the scenario is unlikely, this flawed tie-breaker has reared its ugly head numerous times including a few weeks ago at 2021 Nationals.  Even if it had never happened, it is silly to have a bad rule and pass it off as unlikely, but it has happened, so USTA, pay attention to the ITF and get this one right!

More on the ITF's World Tennis Number

I wrote last year about the ITF introducing the World Tennis Number (WTN) to replace the International Tennis Number (ITN).

Well, it appears it is beginning to be rolled out and a few more details are becoming available.

The LTA (Britain's more or less equivalent to the USTA) has an FAQ on the WTN and it appears they will be adopting it in 2020.  Here are a few items of interest from what list:

• The scale will be 40 to 1, beginners at 40, world class players at or approaching 1
• Ratings will be shown to one decimal place
• Separate singles and doubles ratings, no specific mention of mixed
• Mentions sets, not just wins, taken into account, which implies games or game differential won't be a factor
• Gender and age neutral
• Will incorporate matches played at home and abroad
• Provision for entering scores from personal matches and having them factored in

There is a specific item addressing why the LTA chose WTN instead of UTR.  The summary is they considered UTR focused on American Collegiate Tennis and select High Performance Academies, and thought appealing to and address players of all levels was more important.  They also valued partnering with the ITF and two other Grand Slam nationals (France and the USA).  Like I said before, the WTN is a shot across the bow of UTR.

The ITF also has a WTN FAQ, a few highlights from it:

• The calculation is based on a player's performance relative to the strength of their opponent
• Changes to an opponent's rating may result in a change to your rating, seemingly even if you haven't played more matches
• Implementation of the WTN will be overseen by relevant National Tennis Associations, e.g. the LTA as noted above

What does this mean for players in the USA?  I have not seen anything from the USTA on how they'll adopt it, but my guess is it doesn't affect USTA League or NTRP, at least for the foreseeable future, but the USTA will cooperate with the ITF to feed them match results so the ITF can calculate WTNs for players.  It is also possible the USTA will calculate WTNs for USTA members, but I bet they leave it to the ITF to calculate and just provide results.  We will see.

ITF announces new World Tennis Number to compete with UTR

Regular readers of my blog may remember me writing about the International Tennis Federation's (ITF) International Tennis Number (ITN) in the past.  Well, it appears the ITN will be no more and be replaced by a new World Tennis Number (WTN).

The announcement, made jointly with several national tennis federations including the USTA, FFT (France), and LTA (Britain), doesn't offer many specifics but states that the WTN will

aim to break down one of sport’s key barriers to participation - uneven match-ups - allowing players of all abilities to determine their individual level. This will help players identify opponents and competitions of an appropriate standard and access to more competitive and enjoyable playing opportunities.

It goes on to mention that the WTN (emphasis mine)

will be a powerful enabler in fulfilling the fundamental objectives of increasing participation, and recruiting and retaining players of any age, gender and ability.

I don't believe the prior ITN specifically said whether it was or wasn't gender neutral, but clearly the WTN is intended to be gender neutral, unlike the USTA's NTRP but like UTR.

Some other items of note that I gleaned from reading the site and FAQ:

• Targets players of all levels, but a focus on recreational players.
• Reaffirms being gender and age neutral.
• Separate WTN for singles and doubles.
• No mention of calculation details other than it being "based on the player’s performance in matches relative to the strength of their opponent".  It does say the principals of the calculation will be published for all to see, but it is unclear to what level of detail that will be.
• Late 2019 to early 2020 launch.
• Mentions an on-line community to connect players worldwide.
• Other countries participating in the development include Canada, China, Ireland, Netherlands and Switzerland.

It also discusses adoption of WTN and says national association's existing rating systems are unaffected by introducing the WTN, and the roll out of WTN within a nation is up to the association and it may or may not be adopted along side or as a replacement for the existing system.

To me, while there is no mention of UTR in the press release or site to my knowledge, this is a shot across the bow of UTR.  The ITF is the international governing body for tennis and sees providing a way for players from or within any country to find and play competitive matches to be within their domain.  And to be fair, they created the ITN years ago pre-dating UTR.  Whether it is "international" or "universal" or "world" or "galactic" doesn't really matter, the aim is the same.

But ITN was not widely used (at least from my perspective in the U.S.) and frankly was dated in its algorithm and methodology as they were aiming to make it easy to implement by national associations or organizations 10-15 years ago or more.  In many ways, this sounds like an update to ITN to get it current, and they decided to rebrand it at the same time to make a splash.

What does this mean to USTA League and Tournament players?  My guess is nothing in the short term, I can't imagine there would be a change to use WTN in any way in the next few years.  But the USTA is supporting the WTN so I imagine there will be some collaboration to either support the calculation of the WTN by the ITF, or perhaps even calculate a WTN for players from their USTA play.  Regardless of how the USTA runs leagues and tournaments going forward, it appears players will have a WTN to use and gauge their play by.

What do you think?  Is WTN late to the game?  Or will a rating supported by the ITF and major national governing bodies carry more weight in the end?