📊 How We Calculate Elo Ratings in Our Card Game

Balancing player ratings in a competitive card game isn’t easy — and we’ve been iterating on a custom Elo system that suits Sedma, Semice-inspired gameplay with unique performance metrics.

🎯 What’s new in our Elo system?

✅ Dynamic K-factor
The K-factor controls how fast ratings adjust. Our game adapts K based on your current rating:

• <1200 Elo: K = 40 (new players adjust faster)
• 1200–1800 Elo: K = 32 (normal adjustment)
• 1800–2200 Elo: K = 24 (more stable)
• >2200 Elo: K = 16 (very stable)

✅ Performance-based bonuses
Your Elo update isn’t just win/loss:

• +0.05 per round won by 16 points (max +0.15)
• +0.1 per round won by 24 points (max +0.2)
• +0.03 per round won with 4 and last (max +0.09)

✅ Bad move penalties
Each bad move applies a small malus (–0.02), capped at –0.3 total.

✅ Bonus scaling
If you lose but played well? Your bonuses still apply — but at 10% strength.

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💡 Why this approach?

We want Elo to reflect how you win (or lose), not just the result. A strong performance in a loss should still count for something. Similarly, reckless wins with many bad moves shouldn’t inflate ratings.

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public static void CalculateNewRatings(
ref int ratingA,
ref int ratingB,
bool playerAWon,
int badMovesA,
int badMovesB,
int wonBy16A,
int wonBy16B,
int wonBy24A,
int wonBy24B,
int wonBy4AndLastA,
int wonBy4AndLastB
)
{
    // K determines how sensitive the Elo rating is to each match outcome.
    // Higher K means faster rating changes (good for new players),
    // lower K means more stable ratings (good for experienced players).
    int kA = GetKFactor(ratingA);
    int kB = GetKFactor(ratingB);

    // Bonus and malus coefficients
    const float BonusPer16 = 0.05f;
    const float BonusPer24 = 0.1f;
    const float BonusPer4AndLast = 0.03f;
    const float MalusPerBadMove = 0.02f;

    // Caps
    const float MaxBonus16 = 0.15f;
    const float MaxBonus24 = 0.2f;
    const float MaxBonus4AndLast = 0.09f;
    const float MaxMalus = 0.3f;

    float baseScoreA = playerAWon ? 1f : 0f;
    float baseScoreB = 1f - baseScoreA;

    // Bonus for player A (full if won, 1/10 if lost)
    float multiplierA = playerAWon ? 1f : 0.1f;
    float bonusA =
        Mathf.Min(wonBy16A * BonusPer16, MaxBonus16) +
        Mathf.Min(wonBy24A * BonusPer24, MaxBonus24) +
        Mathf.Min(wonBy4AndLastA * BonusPer4AndLast, MaxBonus4AndLast);
    bonusA *= multiplierA;

    // Bonus for player B (full if won, 1/10 if lost)
    float multiplierB = playerAWon ? 0.1f : 1f;
    float bonusB =
        Mathf.Min(wonBy16B * BonusPer16, MaxBonus16) +
        Mathf.Min(wonBy24B * BonusPer24, MaxBonus24) +
        Mathf.Min(wonBy4AndLastB * BonusPer4AndLast, MaxBonus4AndLast);
    bonusB *= multiplierB;

    float malusA = Mathf.Min(badMovesA * MalusPerBadMove, MaxMalus);
    float malusB = Mathf.Min(badMovesB * MalusPerBadMove, MaxMalus);

    float adjustedScoreA = Mathf.Clamp(baseScoreA + bonusA - malusA, 0f, 1f);
    float adjustedScoreB = Mathf.Clamp(baseScoreB + bonusB - malusB, 0f, 1f);

    double expectedA = 1.0 / (1.0 + Math.Pow(10, (ratingB - ratingA) / 400.0));
    double expectedB = 1.0 / (1.0 + Math.Pow(10, (ratingA - ratingB) / 400.0));

    //Debug.Log($"[ELO CALCULATION]");
    //Debug.Log($"Player A: baseScore={baseScoreA}, bonus={bonusA}, malus={malusA}, adjustedScore={adjustedScoreA}, expected={expectedA}");
    //Debug.Log($"Player B: baseScore={baseScoreB}, bonus={bonusB}, malus={malusB}, adjustedScore={adjustedScoreB}, expected={expectedB}");
    //Debug.Log($"Old Ratings - A: {ratingA}, B: {ratingB}");


    ratingA = (int)Math.Round(ratingA + kA * (adjustedScoreA - expectedA));
    ratingB = (int)Math.Round(ratingB + kB * (adjustedScoreB - expectedB));

    //Debug.Log($"New Ratings - A: {ratingA}, B: {ratingB}");
}

private static int GetKFactor(int rating)
{
    if (rating < 1200) return 40;       // Fast adaptation for new players
    if (rating < 1800) return 32;       // Balanced default for most players
    if (rating < 2200) return 24;       // More stable for advanced players
    return 16;                          // Very stable for top-ranked
}

📝 What’s next?

⚠️ This system is experimental!
We’re actively tuning the coefficients and may adjust:

• How much bonuses/maluses weigh
• When K values change
• How to handle team matches or draws

💬 We want your feedback!
Does this rating feel fair? Did a match leave you thinking the rating change wasn’t justified?
👉 Comment below or reach out — your input helps us refine the system!

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