Mystery box odds calculator
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When a site publishes its odds, a mystery box page tells you two things: what each item is worth and how likely you are to get it. Put those together and you can work out what the box pays back on average, and how often you walk away with less than you paid. This mystery box odds calculator does that maths for you, expected value included, right in your browser. Nothing you type is sent anywhere.
Calculate a box's expected value
Use the value you could actually get back, usually the sell back price shown by the site, not the retail price.
How the numbers are worked out
Expected value is the average value of one opening if you could repeat it forever. Multiply each item's value by its chance, then add the results. Return is the expected value divided by the box price. House edge is whatever is left over: the share of each dollar the platform keeps on average. Chance of getting back less than you paid adds up the odds of every item worth less than the box price.
Worked example
This is an invented box to show the maths. It is not a real box from any platform.
| Item | Value | Odds | Value times odds |
|---|---|---|---|
| Sticker pack | $0.50 | 60% | $0.30 |
| Wireless earbuds | $8.00 | 30% | $2.40 |
| Smartwatch | $40.00 | 9% | $3.60 |
| Games console | $300.00 | 1% | $3.00 |
Add up the last column and the expected value is $9.30, a 93 percent return, so the house edge is 7 percent. That sounds close to break even, but look at the odds: the sticker pack and the earbuds are both worth less than $10, and together they come up 90 percent of the time. Nine openings in ten lose money. The average only looks decent because a rare console pulls it up.
A high expected value does not mean you are likely to win. Always check both numbers.
What this calculator cannot tell you
- It trusts the odds and values you enter. If a site's listed values are higher than what you could really sell the items for, the true return is lower.
- It shows long run averages. Any single opening, or even a few hundred, can land far from the average.
- It ignores fees for shipping, withdrawals and currency conversion, which lower your real return.
- It does not check that results are fair. For that, see how to verify a provably fair result.
Frequently asked questions
What is a good expected value for a mystery box?
There is no good one in the sense of making money: if the return is below 100 percent you lose on average. A higher return simply means you lose less over time. Always look at the chance of getting back less than you paid as well.
Where do I find a box's odds?
Many platforms list the drop chance of every item on the box page before you open it. In our view, a site that hides them is a warning sign, but published odds alone do not prove a box is good value. Our directory shows which platforms list them.
Do free boxes have an expected value?
Yes. With a price of zero every prize is a gain, but free boxes usually come with conditions, such as a deposit before you can withdraw what you win.