calcComboOdds

Calculates the total odds of a combo bet, priced the way the protocol prices it.

Use this whenever you need a combo’s odds for a bet that already exists — to show what it is worth, or to rebuild a payout. For the minimum odds to place a new bet with, use calcMinOdds, which applies slippage on top.

Usage

import { calcComboOdds } from '@azuro-org/toolkit'
 
const totalOdds = calcComboOdds({
  odds: [ 1.5, 2 ],       // leave voided legs out
  createdAt: bet.createdAt,
})

Props

type CalcComboOddsParams = {
  /** the leg odds as the protocol recorded them; a voided leg must be left out by the caller */
  odds: number[]
  /** unix seconds, when the bet was placed - it decides whether the leg odds carry the feed's fee */
  createdAt: number
}

Return Value

string (.toFixed(ODDS_DECIMALS) called on the number)

Why a combo is not the product of its legs

The feed applies its fee to every outcome’s odds. Multiplying N legs that each carry the fee would compound it N times, which is not what the bettor is charged. A combo is therefore priced:

remove the fee from each leg → multiply → apply the fee once to the product

ceil(1.5 / 0.99) * ceil(2 / 0.99) * 0.99  =  3.05
1.5 * 2                                   =  3.00   ← the plain product, too low

The gap widens with every extra leg, so a long combo priced as a plain product is materially understated.

The fee has a start date

The feed did not always apply a fee. For a bet placed before MARGIN_APPLIED_AT the leg odds are raw, so a combo of them really is the plain product — and removing a fee that was never charged, then re-applying it once, would overstate the odds by roughly (1/0.99)^(legs-1).

calcComboOdds branches on createdAt for exactly that reason. Pass the bet’s real creation time; do not default it.

import { calcComboOdds, MARGIN_APPLIED_AT } from '@azuro-org/toolkit'
 
// same legs, different eras
calcComboOdds({ odds: [ 2, 1.75 ], createdAt: MARGIN_APPLIED_AT })      // '3.55...' - fee removed per leg
calcComboOdds({ odds: [ 2, 1.75 ], createdAt: MARGIN_APPLIED_AT - 1 })  // '3.50...' - plain product

Rebuilding a payout

The subgraph records a combo’s odds and payout as the plain product of its leg odds, and never reduces that figure when a leg is voided. So for a bet that has not been redeemed yet, neither settledOdds, odds, potentialPayout nor payout can be trusted for a combo — rebuild from the surviving legs instead:

import { calcComboOdds, isSelectionCanceled } from '@azuro-org/toolkit'
 
const survivingOdds = bet.selections
  .filter((selection) => !isSelectionCanceled({
    selectionResult: selection.result,
    outcomeResult: selection.outcome.result,
    conditionStatus: selection.outcome.condition.status,
  }))
  .map((selection) => +selection.odds)
 
const totalOdds = calcComboOdds({ odds: survivingOdds, createdAt: +bet.createdAt })
const payout = +bet.amount * +totalOdds

Once a bet is redeemed, its recorded payout is the amount actually paid on chain — read that and rebuild nothing. getBetsReport and the SDK’s useBets already apply all of these rules for you.