Backgammon has multiple rating systems — and understanding them helps you track improvement, find appropriate opponents, and know where you stand relative to other players. From the classic FIBS formula to XG’s error-rate analysis, ratings in backgammon measure very different things. Here is how each works.
Key Takeaways
- The FIBS rating system (Elo-based) is the most widely-used online backgammon rating — a new player starts at 1500
- FIBS ratings adjust after each match based on the rating difference and match length
- XG and GNU Backgammon use "error rate" (PR — Performance Rating) as a skill metric — lower is better
- A PR of 0–3 is world-class; 4–6 is expert; 7–10 is strong club player; 11–15 is intermediate
- Match length significantly affects rating stability — longer matches produce more reliable ratings
- Backgammon Galaxy and other platforms use their own Elo variants, but the principles are similar
Types of Backgammon Ratings
Backgammon has two fundamentally different types of ratings:
- Result-based ratings (Elo-style): Based on wins and losses. FIBS, Backgammon Galaxy, and tournament systems use these.
- Error-rate analysis (PR): Based on how accurately you play each position, measured against computer analysis. XG and GNU use these.
Both are useful — but they measure different things.
The FIBS Rating System
FIBS (First Internet Backgammon Server) introduced the most widely-copied backgammon rating formula in 1992. Variants are used by Backgammon Galaxy, DailyGammon, and most competitive platforms.
How It Works
FIBS uses an Elo-based formula adapted for backgammon match play:
- New players start at 1500
- After each match, ratings adjust based on: your rating, opponent’s rating, match length, and result (win or loss)
- Longer matches produce larger rating changes (more reliable results)
- The rating difference between players determines the expected result
The FIBS Formula
The probability of winning for the higher-rated player is:
$$P = \frac{1}{1 + e^{-0.1 \times (D) \times \sqrt{n}}}$$
Where:
- D = rating difference (your rating − opponent’s rating, divided by ~67)
- n = match length (points)
In practice:
- A 200-point rating advantage at 5 points gives ~63% win probability
- The same advantage at 11 points gives ~68% win probability
Rating Changes
After a match:
- Winner gains: roughly 4–8 rating points for a match win against an equal opponent
- Loser loses: the same amount
- Upset: bigger gain for beating a higher-rated player, smaller loss for losing to one
- Expected result: smaller gain/loss when you win what you were “supposed to”
FIBS Rating Benchmarks
| Rating range | Approximate level |
|---|---|
| 1400–1499 | Beginner |
| 1500–1599 | Beginner–Intermediate |
| 1600–1699 | Intermediate |
| 1700–1799 | Strong club player |
| 1800–1849 | Expert |
| 1850–1900 | Master level |
| 1900+ | World-class |
These benchmarks apply to the FIBS scale. Backgammon Galaxy’s scale is calibrated similarly but not identically.
PR: Performance Rating (Error Rate)
PR (Performance Rating), also called error rate, is XG’s (eXtreme Gammon’s) primary skill metric. It measures how closely your play matches the optimal moves calculated by the bot.
How PR is Calculated
After a game or match, XG analyses every position and compares your move to the best move:
- If your move matched the best play: 0 error for that move
- If your move was worse: error = equity difference (how much your play cost)
PR = total equity lost ÷ number of decisions
A lower PR is better (closer to perfect play).
PR Benchmarks
| PR range | Skill level |
|---|---|
| 0.0–2.0 | World-class (top professional) |
| 2.0–4.0 | Expert/Grandmaster |
| 4.0–6.0 | Strong expert |
| 6.0–8.0 | Advanced club player |
| 8.0–10.0 | Intermediate |
| 10.0–15.0 | Improving beginner |
| 15.0+ | Beginner |
Important caveats:
- PR is match-length dependent — shorter matches have higher variance
- PR over a full 25-point match is much more reliable than a 1-point match
- Always compare PR over many games/matches, not single sessions
What Affects PR?
Your PR is impacted by:
- Checker play errors: Most common source of PR loss for beginners
- Cube errors: A single wrong take/drop can cost significant equity (often 0.1–0.3 per decision)
- Position complexity: Complex positions are harder to play correctly
Top professionals regularly achieve PR below 3.0. World-class bots themselves score approximately 0.0 (by definition, since they play optimally).
Tournament Ratings (ABT and USBGF)
The American Backgammon Tour (ABT) and USBGF use their own rating systems for live tournament play:
- Points are earned based on tournament performance and field strength
- Unlike FIBS, tournament ratings often use separate calculations for match strength
- World Backgammon Championship rankings combine multiple tournament results
Backgammon Galaxy Rating
Backgammon Galaxy (the leading online backgammon platform) uses its own Elo variant:
- New players start around 1500
- Calibrates after 10+ matches become more accurate
- Separates ratings by match length (1-point, 3-point, 5-point, 7-point)
- Public leaderboard shows the world’s top-rated active players
Galaxy also uses PR (powered by XG-style analysis) for post-match review.
How to Improve Your Rating
For Elo-Based Ratings (FIBS/Galaxy)
- Play longer matches: More reliable, more rating at stake, more learning per session
- Study regularly: Rating improves with skill — no shortcut
- Don’t play when tired: Mistakes are clustered in tired sessions
- Challenge appropriate opponents: Playing far-higher-rated opponents risks big losses; playing far-lower gives minimal gain
For PR (Error Rate)
- Review all matches in XG: See exactly where equity was lost
- Prioritise cube errors: These are often worth more than checker-play mistakes
- Study problem positions: Find your weakest areas and drill them
- Use rollouts: XG rollouts give the most accurate assessment of controversial positions
Frequently Asked Questions
What is the FIBS rating in backgammon?
FIBS (First Internet Backgammon Server) uses an Elo-style formula where players start at 1500. Ratings adjust after each match based on results, rating difference, and match length.
What is a good backgammon rating?
On the FIBS scale: 1700+ is a strong club player, 1800+ is expert, 1900+ is world-class. Most active online players sit between 1550 and 1750.
What does PR mean in backgammon?
PR (Performance Rating) is an error-rate metric from XG analysis. Lower is better. PR of 0–3 is world-class; 4–6 is expert; 7–10 is strong club level.
Does match length affect ratings?
Yes. Longer matches produce more reliable ratings because variance (luck) averages out. A 1-point match result is highly variable; a 25-point match result reflects skill far more accurately.
Are Backgammon Galaxy ratings comparable to FIBS ratings?
Both use Elo variants starting at 1500, and the scales are broadly similar but not identical. A 1700 on Galaxy is roughly comparable to a 1700 on FIBS, but cross-platform comparisons are not exact.
Can you trust your PR after just one match?
No. PR over a single short match is highly variable. Average PR over 20+ matches is a much better indicator of skill level.
Further Reading
- Backgammon Software & Apps — XG, GNU, and Galaxy in detail
- Backgammon Match Play — How ratings are earned in matches
- Backgammon Tournaments — Where tournament ratings apply
- Is Backgammon Luck or Skill? — Why ratings converge to skill over time
- How to Play Backgammon — Start from the beginning
Sources & References
- FIBS — First Internet Backgammon Server — Original source of the most widely-used backgammon Elo formula (1992).
- Backgammon Galaxy — GBG rating system documentation and benchmark population data.
- eXtreme Gammon (XG) — Source of Performance Rating (PR) methodology and error-rate analysis.
- United States Backgammon Federation (USBGF) — American Backgammon Tour (ABT) rating system documentation.
- Elo, Arpad. The Rating of Chessplayers, Past and Present. Arco Publishing, 1978. Foundation text for all Elo-based rating systems.