By: David Arkow
Novak Djokovic just won his 22nd Grand Slam and his 10th Australian Open. Now that he has tied Rafael Nadal for the Slam record, fans are wondering how much more he has to go. I published an article at the end of 2020 making an analytical case for Djoker as the GOAT. At the time he had 17 Slams, but the argument for his greatness extends beyond pure Slam count with him having the highest peak performance of the Big 3, the most longevity, the best head-to-head record, and the most versatility across surfaces. Based on the aging curves of the Top 15 Open Era players, I projected Djokovic to win 4.4 more Slams from 2021 to 2026. In hindsight, this is definitely an underestimate and now that he has reached 22 and defied traditional aging expectations of the sport, I revisit the question of how many Slams Djokovic will end up with.
Projecting the Future Career of the Tennis GOAT
Since the publication of the article at the end of 2020, Djokovic has won five of the seven Grand Slams he has played in (absent at 2022 Australian and U.S. Open due to COVID vaccination requirements) and won seven other ATP titles adding to his career total of 93. In the original projection, I used ESPN probabilities for Djokovic to win each of the 2021 Slams. From there, I used the aging curves of the Top 15 Open Era players to estimate the average decline in probability for Djokovic at each Slam each year until 2026 (about 2.5% per year). Once I had Djokovic’s probability for all 24 Slams from 2021-2026, that came out to an estimate of 4.4 total Slams. Those estimates could have been miscalculated on three fronts. 1) Djokovic’s probabilities of winning those Slams were actually higher than calculated by ESPN, 2) the projected aging curves, 3) the length of his career. I reform my original projections based on these three criteria.
1. Probability of Winning Future Slams
The peak probability at any tournament for Djokovic winning in the original projection was 33% at the 2021 Australian Open (courtesy of ESPN). Probabilities for tennis tournaments based on simulations are more conservative in their nature since each player must play seven matches to win the title in a field of 128 players. For example, if hypothetically Djokovic is an 85% favorite in each round then he has about a 32% (.85^7) probability of winning the tournament. In reality, as the tournament goes on, competition gets tougher and his probability of winning any given match decreases. If he starts with 95% odds in the first round and his probability of advancing declines by 5% each subsequent round (65% chance once he makes the final), then his probability of winning from the outset is roughly 20%. No matter which way you slice it, it is rare to statistically justify that a player has more than a 50% chance at winning any given tournament. I have used the simulation approach in the past using ATP Elo ratings to give probabilities for all 128 players to reach any respective round at each Slam. In 2021, my Grand Slam simulations gave Djokovic a 19%, 38%, and 23% chance at winning the French, Wimbledon, and the US Open respectively.
Another method of quantifying his probability at the Slams in 2023 is through futures betting odds. In tennis, betting lines inherently boost the probability of the favorites because Vegas has to position themselves favorably. Currently on Vegas Insider, Djokovic’s odds for next four Slams are listed at +162 (French), +110 (Wimbledon), and +137 (US Open), +125 (Australian Open) which translate to 41%, 48%, 42%, and 44% in probability. If someone told you that you could take Djokovic or the field in a straight up bet at this year’s Wimbledon, it would be statistically unsound not to choose the field in a draw of 128 players. Nevertheless, the odds currently have Djokovic at near 50% odds because they need a favorable position. The majority of bets placed are on favorites so while big serving American John Isner (currently ranked No. 42 whose best surface is grass) probably has some outside shot at winning (maybe 0.5%), less than that percentage of bets will be placed on him and on the favorites instead. Surprisingly, you can actually make a futures bet on Isner for Wimleddon this year (which could be his last) at +10000 (0.1% probability). Fans often overestimate the probability of the favorite so as more money comes in on Djokovic, the line shifts and his apparent probability of winning increases. Another example has home crowd favorite Andy Murray listed at +3300 (3%) at Wimbledon even though his odds are likely much lower (Murray is currently ranked 64th and hasn’t made it past the third round in a Slam since hip surgery in 2018). Nevertheless, because Brits like to bet on Murray for fun, his odds seem higher. Granted these are futures odds so once the draw for the tournament is released that could affect the line. For example, if Djokovic is in the same half or even quarter of the draw as Nadal at the French, his odds will likely decrease.
To calculate the probabilities of Djokovic’s next 4 Slams, I will take the midpoint of my 2021 simulations and the futures odds blending a conservative and a bullish estimate to get probabilities of 30% (French), 43% (Wimbledon), 32.5% (US), and 38.5% (Australian).
2. Projecting Aging Curve
Now that I have baseline probabilities for the rest of 2023 and the beginning of 2024 with the Aussie Open, I use historical aging curves to determine how much to dock Djokovic’s probability each year. This is likely the most difficult part of projecting future Slams especially given Djokovic’s game style and his longevity. Is it a linear decline in probability? Is it a sharp drop-off? In my previous article, I graphed the distribution of Slams won by age for all players who have at least five in the Open Era (this sets a baseline for being a very good player among good competition). From that graph, I found the “average peak age” of when the most Slams were won (24) as well as the median age for when these players won their last Slam (31.5). From this I graphed a best-fit line for the decline of these players, seeing what percentage of Slams they lost per year as they aged. It is clear that Djokovic is still at one of his career peaks after winning the 2023 Australian Open. His Elo rating from Ultimate Tennis Statistics is even slightly higher now (2,450) than it was at the end of 2020 (2,380). Therefore, I justify using the previous aging curve with a slightly sharper decline per year (3% decline in probability vs. 2.5%) with a longitudinal shift starting Djokovic’s decline after the 2023 season.
Now the big wildcard in the projection is when Djokovic retires. See the full discussion below about the concerns that could impact the projection but I ultimately chose 2027 as Djokovic’s last year to be a reasonable threat at the Grand Slams when he would be 40 years old. The 2020 article had him being a threat at Slams until 2026 but Djokovic might even be better and healthier now so I add one year onto the original projection. Federer officially retired at 41 and only won 4 Slams after turning 30. Nadal is currently 36 and has won 8 Slams since turning 30. Djokovic is 35 and has won 10 Slams since turning 30.
The final prediction has Djokovic winning 5.74 Slams through 2027. I discuss different factors below that could either lower or boost this number but based on Novak’s current form this seems like a solid projection. My optimistic fan prediction is that he wins 6 more total: 2 more Australian Opens (likely 2024 and one more throughout the remainder of his career), 1 French (in the window when Nadal is not a big threat and Alcaraz is not at his peak yet likely 2023 or 2024), 2 Wimbledons (2023 and one throughout the remainder of his career), and 1 US Open (throughout the remainder of his career).
There are many ways Djokovic’s health could affect these projections and hamper him from accumulating more Slams. He could have a career-ending injury like Federer had with his knee which forced him to retire. Other periodic injuries could force him to miss certain Slams. In his 21-year career so far, he has only pulled out of the 2017 US Open due to an elbow injury. Nadal has missed six and Federer five. Of the Big 3, Djokovic has by far had the healthiest career and the fewest injuries which is surprising considering his very physical game style. This is likely due to his strict fitness, training, and diet regimen. Djokovic’s game style requires speed, agility, and explosiveness so perhaps his decline may be sharper once those skills go since his tactics are reliant on it in contrast to someone like Federer who plays shorter points. Cutting edge age curves in sports look at skill by skill degradation but Djokovic still shows no sign of slowing down. I estimated a linear decline for the aging curve but in reality it could be a sharp drop off where one bad injury severely decreases his odds the following year. There could also be heterogeneity in his decline where he still remains effective on his preferred surfaces of hard or grass but declines on clay. Days after the final of the Australian Open, tournament director Craig Tiley said Djokovic had played with a hamstring tear, but he still only dropped one set en route to his 10th title.
This is the most non-quantifiable off-court aspect, but it plays a big role in how much Djokovic wants to push himself. Chasing records can keep older athletes motivated late into their careers. LeBron James (38 years) just passed Kareem Abdul-Jabbar’s points record (38,388). Alex Ovechkin (37 and 812) is chasing Wayne Gretzky’s goal record (894). Albert Pujols (42) was chasing 700 home runs and Justin Verlander (39) is chasing 300 wins. Once Djokovic passes Nadal which figures to happen soon, how much more will he keep pushing? Knowing Nole, he will likely keep going as he cares a lot about his legacy. As load management has permeated other sports, it is starting to creep its way into tennis with some of the top players choosing to forego certain warmup tournaments to make sure they are as fresh and healthy as possible before a Slam. Federer skipped three French Opens from 2016-2018 for recovery and to maximize his chances of winning Wimbledon. Djokovic does not seem like one to “take his foot off the gas” but he is focused on the Slams this late in his career. Djokovic played 11 tournaments each in 2021 and 2022 down from his usual average of 17 per year. While some of this is likely due to COVID restrictions, it seems likely that we will see Djokovic play fewer of the ATP 250s, 500s, and even 1000s in favor of extending his career as long as possible.
Throughout the past several years, tennis fans have speculated when the next crop of “young guns” will threaten the Big 3. Of the past 76 slams since 2004, only 13 are non-Big 3. Even since 2017 when all of the Big 3 were past their 30s, only 3 (Dominic Thiem, Daniil Medvedev, and Carlos Alcaraz have won the last three US Opens) of the 24 have taken the title. Nevertheless, there has still been a crop of mainstays among the top ranks of the ATP that have challenged Djokovic (mostly at tournaments outside of the Slams in best of 3 set format). I identified three main competition threats to Nole.
First is his contemporary career rival in Rafa as the pair are still technically tied with 22 Slams. The King of Clay should never be counted out at Roland Garros with 14 titles and a career record of 112-3. Currently, Nadal actually is the third favorite by betting odds for the upcoming Roland Garros (+250 behind Djokovic and Alcaraz) likely given his health as he suffered an early second round exit in Melbourne battling an abdominal injury. Given his physical game style and injury history, Nadal likely has another year or two left with his best shot at upping his Slam count coming on clay.
Next we have the established new guard; the tier of players who have established themselves as consistent Top 10 players but are likely at their peak levels given their mid-20s age. Daniil Medvedev (26), Alexander Zverev (25), Andrey Rublev (25), Stefanos Tsitsipas (24), and Casper Ruud (24) have all posed and will likely continue to pose the most challenge to Djokovic over the remainder of his career but they likely don’t have another gear in their game. He has done relatively well against this group with a career record of 29-10 against them.
Lastly we have the new generation of “young guns” who are playing the best tennis of their careers and still might make another jump given their age. Carlos Alcaraz (19), Felix Auger Aliassime (22), and Holger Rune (19) are all inside the Top 10 and are at or near their career highs. Don’t look now but this young core of 3 actually has a combined winning record of 3-2 against Djokovic but that is a small sample size. Waiting in the wings of Federer, Djokovic didn’t win his first Slam until 2008 when he was 20 and his second until 2011 when he was 23. The same story could apply for these youngsters or they just might have to wait until the Serbian star retires to start winning Slams of their own.
Over the past several years, Djokovic has made it more and more clear that he is the greatest men’s tennis player of all-time. As he continues to defy traditional aging expectations and father time, tennis fans wonder how many more Slams he will win. I combine simulated win probabilities and betting odds for Djokovic’s next 4 Slams along with traditional aging curves to estimate what number he will end up at. Based on that analysis, it is likely he ends up somewhere between 26 and 28 Slams with the final count depending on his health, his will, and his competition. Wherever he ends up when he retires, it will be hard to dispute that Novak is the GOAT. But one thing is for certain over the rest of his career. The ball is in his court.