Ties and shared pots
Add split-pot outcomes and distinguish outright win probability from equity.
11 minutes · intermediate · Original Poker4Quant lessonWhat you will learn
Price a heads-up final call when a stated probability of an equal split is possible.
Prerequisites: Expected value as a weighted average · Hand rankings and ties
A tie can have positive incremental value
In a heads-up final call, let the pot before your call be P and the call be C. If the final P+C is split equally, you receive (P+C)/2. Subtract C to get the tie’s net payoff (P−C)/2.
If P=90 and C=30, a tie returns 60 and nets +30 from this decision. The tie does not mean “no money changes hands” because some chips in the current pot were committed before the decision. Whole-hand accounting may tell a different story about past costs.
Equity weights shared outcomes
Let w be outright-win probability, t the tie probability and l=1−w−t the loss probability. Then call EV=wP+t(P−C)/2−lC. Under these exact heads-up, equal-split, no-fee assumptions, equity e=w+t/2 gives the equivalent formula e(P+C)−C.
Multiway pots, uneven split rights, side pots, rake and indivisible odd chips can require different outcome payoffs. Do not reuse half a tie mechanically when the split is not between exactly two equal claimants.
Worked example
P=90, C=30, w=20% and t=20%. Compute call EV and the outright-win threshold if t stays fixed.
- Loss probability is 1−0.20−0.20=0.60.
- Net outcomes are +90 for a win, +30 for a tie and −30 for a loss.
- EV=0.20×90+0.20×30−0.60×30=18+6−18=6.
- With t=20%, the break-even equation is 120w−18=0, so w=15%.
EV is +6. At the threshold, equity is 15%+10%=25%, matching 30/(90+30). Outright-win probability and equity are different numbers.
Common mistakes
- Giving a tie zero incremental payoff without examining the pot.
- Equating equity with outright win probability.
- Using a half-share for a multiway or unequal split.
Keep these ideas
- Compute the net receipt for each split.
- Keep win, tie and loss probabilities exhaustive.
- Use half-tie equity only under the stated equal heads-up split model.