How to work out the margin in an accumulator

Multiply the payback of each leg. If every leg pays back 95% on average, two legs pay back 0.95 x 0.95 = 90.25%, five legs 77.38% and ten legs 59.87%. The big combined odds come with a smaller chance of winning and a larger share kept by the bookmaker.

By BetSmart Kenya Editorial (prepared with AI tools under our editorial policy) · Last updated 2026-10-04

How an accumulator is priced

An accumulator joins several selections into one bet. The decimal odds are multiplied, the stake rides on all of them together, and one losing leg loses the whole bet.

Three legs at 1.90, 2.10 and 1.75 give combined odds of 1.90 × 2.10 × 1.75 = 6.98. A KES 100 stake would return about KES 698 if all three won, and nothing otherwise. If you need to change a price into decimal form first, use the odds converter.

Where the extra margin comes from

Every leg is a price with a margin in it. A single bet passes through one margin. An accumulator passes the same stake through one margin per leg, and the effects multiply in exactly the way the odds do.

Here r is the average payback of a leg and m its margin, with r = 1 ÷ (1 + m). How to measure them for one market is set out in the guide on calculating the bookmaker's margin.

The reason is simple. The average return per shilling on a bet is the true chance of winning times the odds. For an accumulator of independent legs, both the chance and the odds are products, so the average return is the product of the legs' average returns. A row of numbers each a little below 1, multiplied together, falls further below 1 with every factor.

The effect, leg by leg

The table assumes every leg is an even chance (true probability 50%) priced at 1.90, so each leg pays back 95% on average. The stake is KES 100.

The rows are pure arithmetic on an invented price, not a description of any operator's odds.

Two effects that pull the same way

The cost per shilling rises. One KES 100 single costs KES 5 on average in this example. One KES 100 five-leg accumulator costs KES 22.62 on average. The stake is the same, the price of the bet is more than four times higher.

Wins become rare. At ten legs the bet in the table wins about once in 1,024 attempts. Someone placing one such bet a day would wait, on average, close to three years for a win, and that win would return only about 60% of the money staked along the way.

The combination is what makes accumulators costly: long losing runs that look normal, interrupted by an occasional large return that feels like proof the approach works. The average, which is the only thing the arithmetic can speak about, sits well below the stake.

Step by step: measure your own accumulator

1. For each leg, find the margin of its market and the payback r = 1 ÷ S, where S is the total implied probability of that market.
2. Multiply the paybacks of all legs. The result is the average payback of the accumulator.
3. Subtract it from 1 and multiply by the stake. That is the average cost of the bet.
4. Multiply the margin-free probabilities of the legs to see roughly how often the bet would win.

Legs with different margins work the same way. Paybacks of 96%, 94% and 93% combine to 0.96 × 0.94 × 0.93 = 83.92%, an average cost of KES 16.08 per KES 100 staked.

What about splitting the stake into singles?

Staking KES 100 in total on five separate singles in the example passes each shilling through one margin, so the average cost is KES 5. The same KES 100 on the five-leg accumulator has an average cost of KES 22.62. Singles are not cheap either, since their expected value is still negative, as the guide on expected value explains. They are only less expensive per shilling.

None of this is a reason to prefer one kind of bet. It is the information needed to see what a kind of bet costs.

Rules that apply to the bet itself

Regulation 23(1) of the Gambling Control (Conduct of Gambling Operations) Regulations, 2026 requires a licensee to clearly display betting odds, rules and terms applicable to each bet, and regulation 22 requires bookmaking terms and conditions to be in simple language and to state all significant conditions that may affect a punter's decision. How an operator settles an accumulator when a leg is cancelled is a matter for those published terms; read them before, not after.

Small stakes do not change the percentages. A KES 20 accumulator, the least allowed online under section 71(1) of the Gambling Control Act, 2025, has the same average payback as a KES 2,000 one. If small accumulators are adding up over a month, the guide on setting a betting budget and limits shows how to cap the total.