- Maths reviewed by Josh Miller
- Tested by Diana Westfield
A progressive jackpot calculator answers one question: at what size does the jackpot make the game worth it? Take a slot that pays back 92% from normal wins, with a 1 in 50 million chance at £1 a spin. A £2.5 million jackpot adds 5%, so the game is at 97%. It needs £4 million to reach 100%. The free CasinoCalcs calculator does that sum for any game.
How the progressive jackpot calculator works
The jackpot’s share of the RTP is simply what it’s worth divided by how often it lands:
Jackpot RTP = jackpot ÷ (1 in N × bet)
Add that to the RTP from the rest of the game and you have the return right now. The break-even jackpot is the size where the total hits 100%: (100% − base RTP) × N × bet.
Games rarely publish the hit chance. They often publish two RTPs, though: one for the base game and one “including the jackpot at its seed value”. If a game lists 96% overall, 92% without the jackpot and a £1 million seed, the jackpot adds 4 points at seed. That works out to 1 in 25 million at £1. Pick the second option in the calculator and it does this for you.
Is a big jackpot a good bet?
Even above break-even, a progressive is a bad bet for nearly everyone who plays it. The extra value sits in one result that you’ll almost certainly never see. On 1 in 50 million, playing 1,000 spins a day, you’d expect to wait 137 years. Session to session, you play the base game at 92%, and that’s what your bankroll feels.
Two more catches. Many jackpots scale the chance with your stake, so a 20p spin might have a tenth of the chance at £2. And networked jackpots are shared by thousands of players, so the jackpot moving up doesn’t mean it’s “due”. Every spin has the same tiny chance.
To see what a normal slot session costs, try the RTP and house edge calculator. The lottery reality check uses the same long-odds maths.
In Australia the same machines are called pokies, and pokies jackpot odds work the same way: a progressive jackpot is a tiny chance at a big prize, and the calculator gives the odds and how much of the RTP the jackpot accounts for.
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