1. Inputs
2. Input Check
- Leg spacing
- Odds validity
- Overall readiness
Interpretation: easier leg is more likely to win; harder leg is less likely.
3. Odds Conversion
| Leg | Line | Entered Odds | Decimal Odds | Implied Probability |
|---|
Implied probability is raw (1 / decimal odds) — bookmaker vig is not removed.
4. Synthetic Lines — Exact Odds-Dependent Stake Split
| Target Type | Target Line | Easier Weight | Harder Weight | Synthetic Decimal | Synthetic American | Easier Stake | Harder Stake |
|---|
5. Select One Target
Order Ticket
- Target line
- Easier-leg line
- Harder-leg line
- Easier odds entered
- Harder odds entered
- Easier weight
- Harder weight
- Easier stake
- Harder stake
- Synthetic decimal odds
- Synthetic American odds
- Total synthetic return if both legs win
6. Formula & Usage Guide
How to identify the easier leg
The easier leg is whichever side is more likely to win — not necessarily the numerically smaller line. For an Over market, the lower total is easier. For an Under market, the higher total is easier. For a handicap market, it depends on the selected team and the direction of the handicap.
Why the split is odds-dependent (not 50/50)
A simple 50/50 or linear split assumes both legs are equally likely, which is almost never true for adjacent lines. This calculator uses exact settlement-replication weights derived from each leg's decimal odds, so the synthetic price reflects the real probability implied by the market.
Odds conversion formulas
- American → Decimal (positive):
decimal = 1 + american / 100 - American → Decimal (negative):
decimal = 1 + 100 / abs(american) - Decimal → American (≥ 2.0):
american = (decimal − 1) × 100 - Decimal → American (< 2.0):
american = −100 / (decimal − 1) - Implied probability:
probability = 1 / decimal(raw; vig not removed)
Synthetic target lines
Given easier line E and harder line H, where abs(H − E) = 1.0:
- Easier .5 =
E - Easier .25 =
E + 0.25 × (H − E) - Integer .0 =
(E + H) / 2 - Harder .25 =
E + 0.75 × (H − E) - Harder .5 =
H
Exact stake-weight formulas
Let dE, dH be the easier/harder decimal odds, and wE, wH the stake weights (wH = 1 − wE):
- Easier .5:
wE = 1 - Easier .25:
wE = (dH + 1) / (dE + dH) - Integer .0:
wE = 1 / dE - Harder .25:
wE = 0.5 / dE - Harder .5:
wE = 0
Synthetic decimal odds: wE × dE + wH × dH. Stakes: totalStake × wE and totalStake × wH.
Validation & odds-range decision
American odds strictly between −100 and +100 (exclusive) are rejected — standard sportsbook convention has no such price (e.g. there is no valid "+50" American price). Decimal odds must be greater than 1.0. Stake must be a finite number ≥ 0.
Examples: Over, Under, and handicap markets
- Over market: Over 1.5 (easier) / Over 2.5 (harder) — the lower total is more likely.
- Under market: Under 2.5 (easier) / Under 1.5 (harder) — the higher total is more likely.
- Handicap market: Team A −0.5 (easier) / Team A −1.5 (harder) if Team A is favored.
Important note on vig
This calculator uses quoted odds directly and does not remove bookmaker vig (juice/overround) from implied probabilities.