What this calculator works out
This calculator gives your chance of winning at least one prize in a competition or prize draw where there may be several prizes and you may hold several entries. It expresses the answer as a percentage, a one-in figure and odds against, and it also shows the figure you would get by the common shortcut of multiplying your single-prize chance by the number of prizes — so you can see how much that shortcut overstates things.
The hard part of competition odds is not the arithmetic. It is that the one number you need most, the total number of entries, is almost never published. Promoters of UK prize draws must state the number and nature of prizes, and any limit on entries per person, but not how many people entered. So the honest use of this tool is to ask "what would my chance be if there were ten thousand entries, or a hundred thousand?" and to notice how quickly the answer collapses.
It is built for prize draws decided by chance — the "comment to enter" draw, the postal free-entry route, the raffle-style draw with a dozen runners-up. Competitions judged on skill are a different thing entirely and are covered under when not to use it.
The competition and your entries
How the calculation works
For a single prize, your chance is your entries divided by the total. For several prizes, the draw takes entries out of the pool one at a time, and no entry can win twice, so the calculation follows the draw round by round. The cleanest route is to find the chance of winning nothing and subtract it from one.
For each prize drawn, in turn:
chance of missing it = (entries left that are not yours) ÷ (entries left)
Chance of nothing at all = all of those multiplied together
Chance of at least one prize = 1 − chance of nothing
Odds against = (1 − chance) ÷ chanceFive entries in 10,000 with one prize is 5 ÷ 10,000 = 0.05%, which is 1 in 2,000. With ten prizes, the chance of missing all ten is 9,995⁄10,000 × 9,994⁄9,999 × … for ten steps, which comes to 99.501%, so the chance of at least one prize is 0.499% — a hair under ten times the single-prize figure, as you would expect when the prizes are a tiny fraction of the entries.
The multiply-by-prizes shortcut goes wrong when the prizes are a large share of the pool. With 50 prizes among 200 entries, four entries give a real chance of 69% of winning something; the shortcut says 100%. The calculator shows both figures so the gap is visible.
Many promotions limit entries to one, or a handful, per person. That cap does two things. It stops you buying your way to a better chance, obviously — but it also means the total entries figure is close to the number of people who entered, which is often guessable from the size of the audience. A local paper's competition with a one-entry cap and a readership of thirty thousand cannot have more than thirty thousand entries, and in practice will have far fewer. If you enter the cap here, the calculator will tell you when your entries exceed it.
Worked example: five entries in ten thousand
A national drinks brand runs a "scan the code to enter" draw for a single holiday. You have five codes from a multipack, and a guess of 10,000 entries from the size of the promotion.
That is 1 in 2,000, or 1,999 to 1 against.
5 of 10,000 entries are yours, with 1 prize.
| Entries | Chance | One in |
|---|---|---|
| 1,000 | 0.500% | 1 in 200 |
| 10,000 | 0.050% | 1 in 2,000 |
| 100,000 | 0.00500% | 1 in 20,000 |
Exact for a fair random draw. Judged competitions and instant-win promotions do not work this way — see when not to use this calculator.
The chance is 0.050%, or 1 in 2,000 — 1,999 to 1 against. Five codes into a draw that size is a lottery ticket by any other name, and the table shows the point that matters more than the headline: if the promotion actually drew 100,000 entries, which a national brand easily might, the chance is 1 in 20,000.
Change the prizes to fifty — one holiday and forty-nine cases of the product — and the chance of winning something becomes 2.48%, about 1 in 40. The shortcut of multiplying 0.05% by fifty gives 2.5%, and here the two are close, because fifty prizes are a tiny share of ten thousand entries. Where the shortcut breaks is a small promotion with generous prizes: fifty prizes among two hundred entries, with four of them yours, is a real 69% chance of winning something against a shortcut answer of 100%.
How many entries is a promotion likely to get?
Nobody publishes this, so it has to be estimated, and the estimate dominates the answer. Some patterns hold up in practice.
| Kind of promotion | Typical entries | Single-prize chance for one entry |
|---|---|---|
| Local club or society draw, tickets sold by hand | 100 – 1,000 | 1 in 100 to 1 in 1,000 |
| Local newspaper or radio competition with a qualifying question | 500 – 5,000 | 1 in 500 to 1 in 5,000 |
| Independent shop's social media "like and share" draw | 1,000 – 20,000 | 1 in 1,000 to 1 in 20,000 |
| National brand's on-pack or website draw | 50,000 – 1,000,000+ | 1 in 50,000 to worse than 1 in a million |
| Free-entry postal route to a paid national draw | Often a small fraction of paid entries | Frequently the best odds on offer |
The pattern behind the table: entries fall as effort rises. A draw that needs a stamp, a photograph, a form filled in by hand or a correct answer attracts a fraction of the entries of one that needs a click, and your chance rises in proportion. That is the single most useful thing to know about entering competitions, and it is why the free postal route that promoters are obliged to offer is so often the best-value entry in the whole promotion.
These ranges are working estimates from experience, not published statistics. Where a promoter does tell you the entry count — some do, in the winners' announcement — use that.
Understanding the result
Read the one-in figure first. Percentages below 1% are hard to feel; "1 in 2,000" is easier. If the number is in the thousands, you are buying a lottery ticket, whatever the promotion calls itself.
Compare across promotions, not against certainty. The calculator's real use is choosing where to put your effort. Five entries into a national draw at 1 in 20,000 is a worse use of ten minutes than one entry into the local one at 1 in 400.
The shortcut comparison is a sanity check. If the honest figure and the multiply-by-prizes figure are close, the promotion is large relative to its prizes. If they are far apart, the prizes are plentiful and your chance of winning something is genuinely decent — a fifty-runners-up promotion in a small pool can be worth entering even when the top prize is a long shot.
What the promoter must tell you. The CAP Code, which the Advertising Standards Authority enforces, requires a UK prize promotion to state the number and nature of the prizes, any limit on entries per person, the closing date, how winners are chosen and told, and the promoter's name and address. It also forbids exaggerating the chance of winning, and requires prize draws to be conducted by, or under the supervision of, an independent person. A promotion missing those things is not one to put money or effort into.
When not to use this calculator
The lottery rules described on this page are those of the Gambling Act 2005, which applies in England, Scotland and Wales. Northern Ireland has its own legislation and its own limits.
Not for judged competitions. A competition decided on skill — the best caption, the best photograph, the closest guess of the jar of sweets — has no probability attached. The Gambling Act 2005 treats these differently from lotteries precisely because chance does not decide them, and a promoter running one on a "random" basis while calling it a skill competition may be running an illegal lottery. The Gambling Commission's advice note linked below explains the test.
Not for instant-win promotions where a fixed number of winning codes are spread through a product run. Your chance there is winning packs remaining divided by packs remaining, which changes over time and is not published.
Not where entries are weighted — some draws give extra entries for a purchase, a referral or a share. The arithmetic still works if you enter the weighted totals, but you rarely know them.
Not for the money side. A decent chance at a prize you do not want, at a cost of premium-rate texts, may still be a poor deal. The Prize Draw Value Calculator handles that.
Common mistakes
- Multiplying the single-prize chance by the number of prizes. Nearly right when prizes are scarce, badly wrong when they are not. The calculator shows both.
- Guessing the entry total optimistically. If you must guess, guess high. A chance that survives a pessimistic entry count is a real one.
- Ignoring the entry cap. Entries above the limit are usually discarded, sometimes with all your entries. Read the terms.
- Applying it to judged competitions. Skill competitions are decided by people, not by chance.
- Paying to enter when a free route exists. In Great Britain a paid draw normally has to offer a free way in, and it must be no less convenient than the paid one. It is often less used, too.
- Believing "you have been selected". Promoters may not tell you that you have won, or are luckier than others, when you are not, and may not ask you to pay to claim a prize. Anything that does is a scam, not a competition.
Frequently asked questions
What is the difference between a prize draw, a competition and a lottery?
In England, Scotland and Wales, a lottery is where you pay to enter, there is a prize and the winner is chosen by chance; it needs a licence or registration unless it fits one of the exempt kinds. A free draw is the same thing without payment — which is why promotions offer a free postal route. A prize competition is decided by skill, judgement or knowledge, and the test is that the skill element must genuinely stop a significant share of people entering or winning. A promotion that gets this wrong is an illegal lottery, whatever it calls itself.
Do more entries help?
In proportion, yes, for the expected number of prizes. For the chance of winning at least one prize, a little less than in proportion, because your own entries compete with each other for the same prizes. Where entries cost money the expected return generally falls as you buy more. Where a cap applies, entries above it are wasted.
Are competitions with fewer entrants better?
Enormously. Two hundred entries and one prize is 1 in 200; fifty thousand entries and one prize is 1 in 50,000. Competitions that take effort — a photograph, a form, a correct answer, a stamp — attract fewer entries for the same reason they take longer, which makes them the ones worth the time.
How do I know a competition is genuine?
Legitimate UK promotions publish full terms: the promoter's name and address, the closing date, the prizes, how many there are, how winners are picked and notified, and any entry limit. The CAP Code requires all of that and forbids claiming someone has won when they have not. Being asked to pay to claim a prize, or for bank details before any win, is the clearest sign of a scam.
Why does the calculator ask for a maximum entries per person?
Because entering more than the limit usually gets the extra entries thrown out, and sometimes all of them. Entering the cap lets the calculator warn you, and it is also a clue to the total: a one-entry-per-person draw cannot have more entries than it has entrants.
How accurate is the result?
The arithmetic is exact for a fair random draw. The answer is only as good as the entry total you typed in, and that is nearly always an estimate. Treat the result as an order of magnitude — thousands to one, or tens to one — rather than a precise figure.
Is what I enter stored?
No. Everything is calculated in your browser and nothing is transmitted or retained.
Related tools
References
These organisations publish the guidance behind this page.
- Gambling Commission — Prize competitions and free draws: the requirements of the Gambling Act 2005 — where the legal line falls between a lottery, a free draw and a genuine skill competition
- Committee of Advertising Practice — CAP Code section 8, promotional marketing — the rules a UK prize promotion must follow: a clear free-entry route, no exaggerating the chance of winning, independent draws and published winners
- Gambling Commission — Types of lotteries and their regulations — what legally makes a raffle a lottery, and the eight kinds of lottery the Gambling Act 2005 permits
External guidance changes. Check the current position at the source before relying on it for a decision that matters.