What this calculator works out
This calculator gives the chance of winning at least one prize when there are several prizes and you hold several entries, expressed as a probability, a percentage and betting odds.
It handles multiple prizes correctly rather than simply dividing your entries by the total, which overstates the chance when more than one prize is drawn.
Enter your details
Before you rely on the figure
- Total entries is rarely published. Where it is unknown, the calculation shows what a given entry count would mean rather than what your actual chance is.
- The calculation assumes each entry is equally likely to win and that entries are drawn without replacement.
- Skill-based competitions are not random draws. Judged competitions do not work this way at all.
- Some promotions cap entries per person, which changes the arithmetic and is worth reading in the terms.
With one prize, five entries in ten thousand gives a 1 in 2,000 chance. With ten prizes, it is not ten times that — each draw removes an entry from the pool, and you cannot win the same prize twice. The correct calculation works out the chance of winning nothing across all draws and subtracts it from one.
How this calculator works
The chance of winning nothing, subtracted from one:
For each prize i from 0 upwards:
multiply by (entries − your entries − i) ÷ (entries − i)
Chance of at least one prize = 1 − that product
Odds against = (1 − p) ÷ pEach successive term reflects a draw that has already removed one entry from the pool. For small numbers of prizes relative to entries the difference from the simple approach is small; for a promotion with hundreds of prizes it is substantial.
Worked example: five entries in ten thousand
Using the default figures — 10,000 total entries, 5 of them yours, 1 prize:
- Chance of winning: 0.05%
- Odds against: roughly 1,999 to 1
Now raise it to 50 prizes. The chance becomes about 2.2% — forty-four times better, not fifty times, because of the overlap between draws. It is still a 1 in 45 chance from five entries, which is the honest scale of most multi-prize promotions once the numbers are written down.
Common mistakes
- Multiplying the single-prize chance by the prize count. It overstates the result.
- Assuming the entry total. It is rarely published and heavily affects the answer.
- Applying it to judged competitions. Skill-based entries are not random draws.
- Ignoring entry caps in the terms. They limit what more entries can achieve.
- Treating a small probability as a plan. A 1 in 2,000 chance is a 1 in 2,000 chance.
Frequently asked questions
What is the difference between a prize draw and a lottery?
In Great Britain, a lottery involves paying to enter a game of pure chance and generally requires a licence from the Gambling Commission. Free prize draws and genuine skill competitions fall outside that, which is why promotions offer a free entry route or include a qualifying question. The distinction is legal rather than cosmetic.
Do more entries help?
Proportionally, yes — ten entries are ten times better than one. But ten times a very small number is still a very small number, and where entries cost money the expected return usually falls as you buy more. The Prize Draw Value Calculator shows the money side of that.
Are competitions with fewer entrants better?
Mathematically, considerably. A local competition with two hundred entries and one prize gives odds far better than a national one with fifty thousand. Competitions requiring effort — a photograph, a caption, a longer form — attract fewer entries for the same reason they take longer to enter.
How do I know a competition is genuine?
Legitimate promotions publish full terms including the closing date, the prize, how winners are chosen and notified, and the promoter's name and address. Requests for payment to claim a prize, or for bank details before any win, are the clearest warning signs. The Gambling Commission publishes guidance on what is and is not permitted.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- Gambling Commission — the legal distinction between prize draws, competitions and lotteries
- GOV.UK — consumer protection rules on promotions and prize draws
Sources are checked at publication and can change — how I choose and check references.