Popular opinion: CF ratings are unrelated to your IOI results. CF contests differ significantly from IOI contests.

❌ False!

Unpopular opinion: A contestant's Codeforces rating is more predictive of their final IOI result than their score on Day 1 is of their score on Day 2.

✅ True!

A higher CF rating, with a gap of at least 50, correlates with an 84% chance of achieving a better placement at IOI. The relationship between IOI placement and CF rating is strongly connected. The Pierson Correlation Coefficient for these two factors is -0.813. At the same time, the Pierson Correlation Coefficient between the scores of day 1 and day 2 of IOI is 0.804.

A side note for IOI participants: If you performed poorly on the first day, just think of it as a single bad Codeforces contest—you can always do better next time! You can likely compensate on the second day. Likewise, if you did a great job on Day 1, don't relax too much; the next day is a new challenge. The 0.804 coefficient shows a strong connection, but just as CF rating!

Correlation between CF rating and IOI placement

Here are the statistics on CF ratings for each medal:

Additionally, I've discovered an interesting correlation: participants' ratings one year before IOI also correlate with their final ranks; the Pierson Correlation Coefficient is 0.70.

Correlation between CF rating a year before IOI and IOI placement

Based on this insight, I’ve trained a model that can predict your placement at IOI. If you’re curious about your predicted placement for IOI 2026, leave a comment! Note that as time passes, the model can determine your place more accurately. Feel free to comment again in six months to see the updated prediction.

You can check out a similar blog post for IOI 2024 here.

I predicted results for some people in the above blog.

Update: If you want to make the data more complete, please comment if you know someone from this gist.