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Rankings — Full Details

every multiplier · every penalty · every edge case

Two Numbers, Two Purposes

Every player carries two scores in the database, and they are computed independently from the same approved-game event:

Rating (players.rating) — an Elo-flavored number that drives the Power Rankings leaderboard. Can go up and down. Both winners and losers move.
Total Points (players.total_points) — a lifetime NMJL-style payout total shown on each player's own page. Monotonically non-decreasing. Only the winner of a hand gains points; losers never lose total points.

Total Points answers "how much would I have collected at a real table over my whole mahjong career?" Rating answers "who's actually playing well lately?"

Current Default Values

All of these live in the app_settings row and are editable from the Admin → Settings tab without a redeploy:

starting_rating

1000

k_factor

jokerless_bonus

concealed_bonus_multiplier

0.2

discard_penalty_multiplier

2.0

base_win_points

25 (legacy, not currently in formula)

Line Points (NMJL Card)

Every win is tied to a specific line on the current National Mah Jongg League card. That line carries:

point_value — typically 25, 30, 35, 40, 50, 60, or 75. Hard hands pay more.
concealed_only — line can only be won concealed. Triggers the concealed multiplier automatically.
is_singles_and_pairs — line cannot legally use jokers, so the jokerless bonus is suppressed (otherwise it would be free money).

linePoints below always refers to the point_value of the exact line the winner declared.

Rating — Per-Game Formula

Step 1 — Expected score (Elo)

avgOpponentRating = mean(rating of each loser at the table)
winnerExpected = 1 / (1 + 10^((avgOpponentRating − winnerRating) / 400))

Standard Elo against the average of opponent ratings. A 400-point gap = ~10× expected win odds.

Step 2 — Winner gain

concealedPart = concealed

? linePoints × (1 + concealed_bonus_multiplier)

: linePoints

jokerlessForRating = (used_jokers || isSinglesPairs)

? 0

: jokerless_bonus

winnerRatingGain = concealedPart

+ jokerlessForRating

+ K × (1 − winnerExpected)

Step 3 — Loser losses

baseLoss = (K × winnerExpected) / numLosers

for each loser:

if loser.id === discarder_id:

loss = baseLoss × discard_penalty_multiplier

else:

loss = baseLoss

Note: the discarder pays a 2× share, but the other losers are NOT discounted. The total rating change of the table is not zero-sum — line points and bonuses are added on top of the Elo exchange.

Special cases

Self-pick: no discarder. Every loser pays baseLoss equally.
Wall game: is_wall_game = true. No winner, no discarder. Zero rating change for everyone. Still counted as a game played.
Discard win with no discarder recorded: falls back to a flat split (every loser pays baseLoss).

Worked Example

4-player table. Winner rated 1050. Three losers rated 1000, 980, 1020 (avg 1000). Winner declared a 35-point line, not concealed, used a joker. Lost the hand off a discard from the 980 player.

winnerExpected = 1 / (1 + 10^((1000 − 1050)/400)) ≈ 0.571

concealedPart = 35

jokerlessForRating = 0 (used a joker)

winnerRatingGain = 35 + 0 + 16 × (1 − 0.571) ≈ 35 + 6.86 = +41.86

baseLoss = (16 × 0.571) / 3 ≈ 3.05

discarder (980) loses 3.05 × 2.0 = −6.10

other two losers each lose −3.05

Same hand self-picked instead: all three losers would have lost ≈ −3.05.

Total Points — NMJL Payout Logic

Added to players.total_points for the winner only. Models how chips would actually change hands at a real table:

if self_pick:

winnerPoints = numLosers × 2 × linePoints

else if discarder_id is set:

winnerPoints = 2 × linePoints (from discarder)

+ (numLosers − 1) × linePoints (from each other loser)

else (fallback):

winnerPoints = numLosers × linePoints

if !used_jokers && !is_singles_and_pairs:

winnerPoints += jokerless_bonus

Concealed multiplier is not applied to total points — only to rating. This keeps the total points number numerically aligned with NMJL table-payout math.

"Games Played" & Win Rate

Every approved game increments the games-played count for every participant listed in game_participants, including wall games.
Win rate = wins ÷ games_played. Wall games count in the denominator but never in the numerator, so wall-heavy nights gently drag your win rate down — which matches table reality.
Pending and rejected games do not count for anything.

What We're Not Tracking (Yet)

To keep submission fast and friendly, we deliberately skip several optional NMJL penalties:

Feeding a 2-exposure hand (−10) or 3-exposure / 2-exposure-on-quint hand (−25).
Misnamed discard penalties (−10 to −25 depending on whether it gave mahjong).
Dead-hand penalties on wall games (−10).
Per-section difficulty multipliers (the column exists on nmjl_sections but isn't currently fed into the formula).

If we ever want them, they belong in the admin approval flow — not on the submitter — so the table consensus is what gets recorded.

Tunable Knobs (Admin)

All editable on Admin → Settings, applied immediately to all future approvals. Past games keep the deltas they were approved with.

starting_rating — what new players begin at.
k_factor — how aggressive the Elo swings are. Higher = bigger upsets, more volatility.
jokerless_bonus — flat reward added to both rating and total points for a no-joker win.
concealed_bonus_multiplier — multiplies linePoints in the rating formula for concealed-only hands. Default 0.2 = +20%.
discard_penalty_multiplier — how many baseLoss shares the discarder eats. Default 2.0.

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