Mines game maths: how Vault Grid odds, payouts and cash-outs work

Vault Grid is a mines game on a 5×5 grid: 25 tiles, between 1 and 24 hidden mines, and a multiplier that grows with every safe tile you open. The multiplier is the fair price of the risk you have taken, times 0.97, so the house edge is 3% wherever you stop. This guide shows the hypergeometric formula, a worked table and the cash-out maths.

This article is part of our slot guides, written to explain the maths and mechanics behind every spin.

The table gives, for four mine counts, the chance of surviving s safe picks in a row and the multiplier the game pays for them. Both come straight from the formulas below, and the multiplier is floored to two decimals as in the server code.

Source: the round-settlement code of the VegasSlots Originals, computed on 24 October 2026. Play-money XP only.

How does Vault Grid place the mines?

Before your first click, the server draws a secret seed and shows you its SHA-256 hash. It then hashes the seed, your client seed and a counter, and uses the first eight hexadecimal digits of the result to start a shuffle of the 25 tile numbers. The first M tiles of the shuffled list are the mines, where M is the mine count you chose.

• The board does not change while you play, and opening a tile moves nothing.
• When the round ends, the seed is revealed, and “Verify last round” rebuilds the shuffle in your browser.
• Eight hex digits give about 4.3 billion starting values, comfortably more than the largest number of layouts: 25 tiles with 12 mines give 5,200,300.

What are the chances of surviving s safe picks?

With M mines among 25 tiles, the first pick is safe with probability (25 − M) / 25. After one safe tile there are 24 tiles left and still M mines, so the second pick is safe with (24 − M) / 24, and so on. Multiplying the steps gives the hypergeometric probability:

P(s safe picks) = C(25 − M, s) / C(25, s) = (25−M)/25 × (24−M)/24 × … × (25−M−s+1)/(25−s+1)

For 3 mines and 3 picks that is 22/25 × 21/24 × 20/23 = 0.8800 × 0.8750 × 0.8696 = 66.96%. A round with 3 mines is survived up to the very last safe tile only if all 22 picks are safe, which happens with probability 1 / C(25, 3) = 1 in 2,300.

How is the payout per pick derived from the code?

The server starts with 0.97 and, for each safe pick i from 0, multiplies by (25 − i) / (25 − M − i). That is the inverse of the survival probability times 0.97, floored to cents:

multiplier(M, s) = floor( 100 × 0.97 × C(25, s) / C(25 − M, s) ) / 100

With 3 mines the first three picks pay ×1.10, ×1.25 and ×1.44. The payout is your stake times the multiplier, rounded down to whole XP.

The ratio between two neighbouring multipliers is (25 − s) / (25 − M − s), which is exactly the inverse of the chance that the next tile is safe. Each extra pick is priced at its true odds, and the whole 3% is taken once, at the start.

What house edge does that imply?

Chance times multiplier is 0.97 at every stopping point before rounding. Two rounding steps then trim the return a little, and the amount depends on where you stop and on your stake.

• The multiplier is cut to cents. With 3 mines and 2 picks, the exact figure is 0.97 / 0.77 = 1.2597 and the game pays ×1.25, so the return is 0.77 × 1.25 = 96.25%.
• The payout is cut to whole XP. A 5 XP stake at ×1.10 is 5.5, which pays 5 XP, so a survived first pick returns the stake and nothing more. With 3 mines that is a return of 88% on a 5 XP stake, against 96.8% on a 100 XP stake.
• For a 3-mine board and 4 or more picks (×1.67 and up), cutting the multiplier to cents leaves the exact return between 96.5% and 97.0%.

The headline edge is therefore 3%, and small stakes at low multipliers can lose more to rounding. A 5 XP stake only shows a profit once the multiplier reaches ×1.20, which pays 6 XP.

When should you cash out?

Mathematics gives no best stopping point. Suppose you hold s safe picks at multiplier m. The next pick is safe with probability p, and it multiplies your payout by 1 / p, so continuing is worth p × m / p = m. Stopping and continuing have the same expected value, apart from the rounding described above.

What changes is the shape of the result. With 5 mines you have two typical choices, and both return about 97%:

• Stop after 3 picks and collect ×1.95, with a 49.57% chance.
• Stop after 8 picks and collect ×8.32, with an 11.65% chance.

Decide your exit before the first click, using the table above, and base it on how much XP you can afford to see disappear. Our volatility guide describes the same trade-off for slots, and the RTP guide explains why the 97% only shows over many rounds.

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Frequently asked questions

How many mines can I choose in Vault Grid?

Any number from 1 to 24 on the 25-tile grid. With 24 mines there is a single safe tile, which pays ×24.25.

What is the formula for the Vault Grid multiplier?

It is 0.97 × C(25, s) / C(25 − M, s), floored to cents, for s safe picks and M mines. The result is the inverse of your survival chance, reduced by the 3% edge.

Is it better to play with few mines or many?

Neither gives a better average. Few mines give frequent small gains and many mines give rarer, larger ones, at the same 97% return before rounding.

Why did a safe first pick pay only my stake back?

The payout is rounded down to whole XP. A 5 XP stake at ×1.10 is 5.5 and pays 5. Larger stakes lose far less to this rounding.

Can I turn Vault Grid XP into money?

No. XP has no cash value and cannot be bought or withdrawn. Real-money mines games use a similar pricing idea, with their own published return.

Playing responsibly

Vault Grid is free and uses play-money XP, but the same maths applies to real-money mines games, where the edge is taken from every round. You must be 18 or older to play for money. Set a deposit limit and a time limit before you start, never chase losses and stop when it is no longer fun. Our responsible gambling page lists support, and every regulated market has a free, confidential helpline.

More in the guides: how crash games work and Plinko odds. Try them free in the arcade as Rocket Rush and Neon Drop.