This page explains exactly how we build, test and check every betting calculator on Odds Calculator Ireland. If you are wondering why a number on our site does not match a bookmaker by a cent or two — this is the page to read.
Formulae we use
- Decimal odds: return = stake × decimal odds. Profit = return − stake.
- Fractional odds: decimal = (numerator ÷ denominator) + 1.
- American (moneyline): positive: decimal = (price ÷ 100) + 1; negative: decimal = (100 ÷ |price|) + 1.
- Each-way: stake is split in two equal parts — win part returns at full odds, place part at (decimal odds − 1) × place fraction + 1.
- System bets (Trixie, Yankee, Lucky 15…): we enumerate every combination of selections of the correct size and settle each one as a parlay using the win/lose/void status you pick.
- Lucky bonuses: 20% bonus if all selections win; 3× odds bonus on a single winner. We follow the most common bookmaker convention — your bookmaker’s terms may differ.
- Matched betting: lay stake = (back stake × back odds) ÷ (lay odds − commission). For free bets (SNR) we use (back stake × (back odds − 1)) ÷ (lay odds − commission).
- Dutching: stake on each selection = total stake × (1 ÷ decimal odds) ÷ Σ(1 ÷ decimal odds).
- Arbitrage: a sure bet exists when Σ(1 ÷ decimal odds) < 1. Stake distribution uses the same formula as dutching.
- Kelly Criterion: f* = (b × p − q) ÷ b, where b = decimal odds − 1, p = your win probability, q = 1 − p.
- Forecast / Tricast: we use a simplified Computer Straight Forecast approximation. Tote-style returns by the Irish Tote may differ; use the result as a guide.
How we test
Every calculator is tested against three independent sources: a hand-worked example, an industry-standard reference (e.g. the official Lucky 15 settlement table for system bets), and at least one settled bookmaker bet slip. We re-run all tests whenever we change a calculator.
Rounding
We round results to two decimal places at the final step. Bookmakers occasionally round each leg independently, which can produce a one-cent difference. This is not a bug on our side — we explain this in detail on each calculator page.
What we do not cover (yet)
We do not currently support Tote returns (live SP), Asian handicap calculators, or bet builder pricing. These are on our roadmap.