ELO rating
How the rating worksSudoku ELO in one minute
Sudoku ELO is a skill rating earned in head-to-head sudoku matches. Two players race to solve the same puzzle and the winner takes rating points from the loser. Beating a higher-rated opponent pays more than beating a lower-rated one, so the number settles on your real strength — not on how much you play.
On Sudoku Corner everyone starts at 1200 in each division (beginner, intermediate, expert). New accounts move fast with K = 40 for the first 30 games, then settle to K = 20. Mistakes and hints don't change the rating directly; they cost time, and time decides the match.
There are two numbers: global ELO, a lifetime rating that never resets, and season (league) ELO, which restarts every month for the SC League. Both move by the same amount after a match.
Play a ranked match to get your rating, or see the current leaderboard.
What is ELO?
ELO is a way to measure relative skill, created by the physicist Arpad Elo for chess. Your rating is one number: higher means stronger. Win against a strong opponent and you gain a lot; lose to a weaker one and you lose a lot. Over time the rating settles where your skill is.
Every new player starts at 1200. That's the average. Wins take you above it, losses below.
Two ratings — per division
Season ELO
Resets to 1200 at the start of every month, so everyone begins equal. Decides your place on the monthly leaderboard.
Global ELO
Never resets. Your all-time rating from every ranked match, shown on your profile.
Both are kept separately for each division. Beginner matches only change your beginner rating — a strong expert still starts fresh in beginner.
How it's calculated
- Expected score. How likely you are to win from the two ratings. Equal ratings: 50 % each. A 200-point gap gives the stronger player about 76 %.
E = 1 / (1 + 10(opponent − you) / 400) - Actual result. 1 for a win, 0 for a loss, 0.5 for a draw.
- Rating change. The difference, times the K-factor.
Δ = K × (result − E)
The K-factor
K sets how far one match can move your rating. New players use a higher K so they reach their level quickly; then it drops for a steadier rating.
| Player | Rated games | K | Max change per match |
|---|---|---|---|
| New | fewer than 30 | 40 | ±40 |
| Established | 30 or more | 20 | ±20 |
K is tracked per division: with 50 expert games but 5 beginner games you have K = 40 in beginner and K = 20 in expert.
Examples
Example 1 · Equal opponents
Alice1200 · K 20 · 50 % to win
vsBob1200 · K 20 · 50 % to win
- Alice wins: Alice +10 → 1210 · Bob −10 → 1190
- Bob wins: Bob +10 → 1210 · Alice −10 → 1190
With equal ratings the winner gains exactly what the loser loses.
Example 2 · Big rating difference
Carlos1400 · K 20 · 85 % to win
vsDiana1100 · K 20 · 15 % to win
- Carlos wins: Carlos +3 → 1403 · Diana −3 → 1097
- Diana wins: Diana +17 → 1117 · Carlos −17 → 1383
When the favourite wins, few points move — the system expected it. An upset moves many.
Example 3 · Small rating gap
Eva1300 · K 20 · 64 % to win
vsFrank1200 · K 20 · 36 % to win
- Eva wins: Eva +7 → 1307 · Frank −7 → 1193
- Frank wins: Frank +13 → 1213 · Eva −13 → 1287
Example 4 · New player
Grace1200 · K 40 · 30 % to win
vsHenry1350 · K 20 · 70 % to win
- Grace wins: Grace +28 → 1228
- Henry wins: Henry +6 → 1356 · Grace −12 → 1188
Grace is new (K = 40), so her rating moves about twice as fast and finds her real level sooner.
Win probability by rating gap
| Gap | Stronger wins | Weaker wins | If stronger wins | If weaker wins |
|---|---|---|---|---|
| Equal | 50 % | 50 % | +10 / −10 | +10 / −10 |
| +50 | 57 % | 43 % | +9 / −9 | +11 / −11 |
| +100 | 64 % | 36 % | +7 / −7 | +13 / −13 |
| +150 | 70 % | 30 % | +6 / −6 | +14 / −14 |
| +200 | 76 % | 24 % | +5 / −5 | +15 / −15 |
| +300 | 85 % | 15 % | +3 / −3 | +17 / −17 |
| +400 | 91 % | 9 % | +2 / −2 | +18 / −18 |
For established players (K = 20). New players (K = 40) see about double.
Monthly seasons
At the start of each month a new season begins and every season ELO goes back to 1200 in every division.
- Fair competition — everyone starts equal, so new players can reach the top too.
- Fresh start — a bad month doesn't follow you.
- Monthly leaderboard — compete for the season ranking and the champion badge.
- Global ELO stays — your long-term progress is never reset.
Tips for climbing
- Play consistently. The rating gets more accurate with games; the first 30 move it faster.
- Don't fear stronger opponents. Losing to someone 200+ above you costs little; beating them pays well.
- Avoid errors. The error limit is an automatic loss, and each error costs time.
- Practise in solo sudoku. It never touches your rating.