The house edge on a slot is the share of every stake the game keeps on average: 100% minus the RTP. Your expected loss is the total you stake multiplied by that edge, and the total you stake is your stake per spin multiplied by the number of spins, which is why speed and stake matter as much as the percentage.
This guide puts numbers on that. All game figures here are illustrative round numbers; each game page on this site shows its own published RTP.
The two formulas you need
House edge = 100% − RTP
Expected loss = total staked × house edge
And because total staked builds up spin by spin:
Total staked = stake per spin × spins
So, combined:
Expected loss per hour = stake per spin × spins per hour × house edge
Note that “total staked” is not the same as what you deposit. If you deposit £50 and keep playing with your wins, the same money can be staked many times over. The house edge applies to every pound that goes through the game.
The 1,440 spins an hour ceiling
Since 31 October 2021, online slots on GB-licensed sites must take at least 2.5 seconds per game cycle. An hour has 3,600 seconds, so:
3,600 ÷ 2.5 = 1,440 spins an hour at most
Most people play slower than that, pausing, changing games and watching features. But it sets a hard ceiling on how fast money can go through a GB online slot. Our game design rules page covers the other requirements introduced at the same time.
Expected loss per hour: worked examples
All rows assume an illustrative 96% RTP, so a 4% house edge.
| Stake per spin | Spins per hour | Total staked | Expected loss (4%) |
|---|---|---|---|
| 20p | 600 | £120 | £4.80 |
| £1 | 600 | £600 | £24.00 |
| £1 | 1,440 | £1,440 | £57.60 |
| £2 | 1,440 | £2,880 | £115.20 |
| £5 | 1,440 | £7,200 | £288.00 |
The £2 and £5 rows correspond to the maximum online slot stakes in Great Britain: £2 per spin for 18 to 24 year olds and £5 per spin for players aged 25 and over. See stake limits.
Changing the RTP
Now hold the stake and speed steady, £1 a spin and 600 spins an hour, and change the RTP.
| RTP | House edge | Total staked | Expected loss per hour |
|---|---|---|---|
| 97% | 3% | £600 | £18 |
| 96% | 4% | £600 | £24 |
| 94% | 6% | £600 | £36 |
| 92% | 8% | £600 | £48 |
A couple of percentage points of RTP makes a real difference over time. Choosing a higher-RTP version of a game you would play anyway lowers the cost. Check the figure at your site, as many games come in several versions; our RTP guide explains how.
You can run your own numbers in the RTP calculator.
Expected loss is an average, not a forecast
These figures describe what happens on average across a huge number of hours. A single hour can end much further down, or in profit, depending on volatility. On a high volatility game, the typical hour ends worse than the average, balanced by rare hours that end far better.
That cuts both ways. A winning session does not mean the maths has stopped applying; it means you were on the better side of the spread that time.
How slots compare with roulette
House edge is easiest to compare with games whose maths is fixed and public.
| Game | House edge |
|---|---|
| European roulette (single zero), standard bets | 2.70% |
| American roulette (double zero), most bets | 5.26% |
| Slot at 96% RTP (illustrative) | 4% |
| Slot at 94% RTP (illustrative) | 6% |
The roulette figures come straight from the wheel. A single-zero wheel has 37 pockets and pays as if there were 36, so the edge is 1 ÷ 37, about 2.70%. A double-zero wheel has 38 pockets, so the edge on most bets is 2 ÷ 38, about 5.26%.
But the percentage is only half the story. A roulette table might complete far fewer spins per hour than a slot. Using illustrative figures, compare:
- Roulette: £1 a bet, 40 spins an hour, 2.70% edge. £40 staked, expected loss about £1.08.
- Slot: £1 a spin, 600 spins an hour, 4% edge. £600 staked, expected loss £24.
Even with a similar edge, the speed of slots means far more money goes through them in the same time. That is the main reason slots cost more per hour than most table games, and why the 2.5 second minimum exists.
Why there is no way round it
Every licensed slot has an RTP below 100%. So every formula on this page ends in a loss on average, whatever the stake, speed or game. Changing stake between spins, switching games or playing at different times does not change the edge; only the amount staked changes, and with it the expected loss.
The useful thing the maths gives you is a price. If you know roughly what an hour costs at your usual stake, you can decide whether that price is worth the entertainment, and set a limit to match.
The short version
- House edge = 100% − RTP; a 96% RTP game keeps 4% on average.
- Expected loss = stake per spin × spins × house edge.
- GB online slots cannot exceed 1,440 spins an hour (3,600 ÷ 2.5).
- At £1 a spin and 600 spins an hour, a 4% edge costs about £24 an hour on average.
- European roulette’s edge is 2.70%, but slots run far faster, so cost more per hour.
- Expected loss is an average; real sessions vary widely around it.
Questions people ask
What is the house edge on a slot?
It is 100% minus the game's RTP. A slot with a 96% RTP has a house edge of 4%, meaning the game keeps 4p of every £1 staked on average over the long run.
How do I work out my expected loss on a slot?
Multiply the total amount you stake by the house edge. Total staked is your stake per spin multiplied by the number of spins, so £1 a spin for 500 spins at a 4% edge is £500 × 0.04 = £20.
Do slots have a higher house edge than roulette?
Often, yes. Single-zero European roulette has a house edge of 2.70% on standard bets, while many slots have house edges of several per cent. But slots also run much faster, which affects the cost per hour more than the percentage alone.
How many spins an hour can you play on a GB online slot?
No more than 1,440. GB online slots must take at least 2.5 seconds per game cycle, and 3,600 seconds divided by 2.5 is 1,440.
Next guide: Near Misses and Losses Disguised as Wins in Slots