Expected loss is the amount a game is built to keep from you, on average, over the money you put through it. Pick a game preset or type an RTP figure in directly.
How it works
total staked = stake per round × rounds per hour × hours
house edge = 1 − RTP
expected loss = total staked × house edge
Nothing here is an estimate or a model. Given those four inputs the answer is arithmetic, and you can check it on paper: 20p a spin, 600 spins an hour, one hour, 96% RTP gives £120 staked and £4.80 expected loss.
Choosing realistic inputs
Rounds per hour is the number people get most wrong, and it dominates the result. On mobile, a slot with the minimum 2.5-second spin duration that Great Britain requires tops out around 1,400 spins an hour if you never pause; in practice, with reading the screen and the odd cup of tea, several hundred an hour is normal. Live dealer tables are slower by an order of magnitude — a real roulette wheel gets through something in the region of 40 to 60 spins an hour, while an RNG roulette table with no dealer runs many times faster. If you want a figure for your own play rather than a guess, time five minutes of it and multiply.
RTP is usually published in the game's information or paytable screen. Take it from the game you are actually playing rather than from a general figure, because the same title is often supplied to operators at several different RTP settings — see house edge and RTP by game.
Stake per round should be your typical stake, not your smallest. If you raise stakes after a losing run, your effective average is higher than you think and so is the bill.
What the number is, and what it is not
Expected loss is a mean. It is the average of every way the session could go, weighted by how likely each is. Two things follow, and both matter:
It is not what will happen. On a high-volatility slot the single most likely outcome of a short session is to lose more than the expected loss, because the average is propped up by rare, large wins that most sessions do not get. The median result is worse than the mean. That asymmetry is covered properly on variance and session results.
It is also not a ceiling. Expected loss is what the game takes from the money you put through it; what you can lose is limited only by what you deposit. The calculation tells you the price of the ride, not the worst case.
Using it as a budget rather than a forecast
The most useful way to read the output is backwards. Decide what an evening's entertainment is worth to you — the same way you would price a cinema ticket or a round of drinks — then work out what stake and speed produce that figure, and set a deposit limit at it. £5 an hour is 20p spins at 600 an hour on a 96% game. £20 an hour is the same game at 80p. Neither is more or less "correct"; they are different prices for the same product, and they are yours to choose before you start rather than discover afterwards.
Setting the limit is the part with teeth. Every Great Britain-licensed operator must offer deposit limits, and reductions take effect straight away while increases are held back for a cooling-off period. How the limits and blocks actually work explains what each control does and does not cover.