Progressive jackpot slots: how the prize grows and what it costs

Where the jackpot money comes from

In a progressive game, a fixed percentage of each bet is diverted into one or more prize pools. Part of that contribution builds the visible jackpot and part usually funds the “seed”, the amount the jackpot resets to after a win. Nothing is added by the casino beyond what players have staked.

What it does to RTP

A slot’s total theoretical return is the base-game return plus the jackpot contribution. If a game is published at 94% overall with a 4% jackpot contribution, ordinary play returns about 90% and the remaining 4% is returned, eventually, to jackpot winners. For nearly every player in nearly every session, the base figure is the one that applies.

The Gambling Commission’s guidance on live monitoring says games connected to progressive systems should be measured at base-game level, with jackpot frequency and average size checked separately, because jackpots are infrequent and large enough that measuring their RTP may not be feasible.

Types of progressive

Many games run several tiers at once, such as mini, minor, major and grand, each with its own contribution rate and seed.

Does a bigger jackpot make the game better value

As the pool grows, the average value of the next jackpot win rises while the price of a spin does not. In principle a very large jackpot improves the expected return. In practice the published figures needed to work out the break-even point, such as contribution rates and hit probability, are rarely available to players, and the result still depends on one extremely unlikely event.

Must-drop jackpots come closest to being predictable, because the prize must fall before a known ceiling. They attract more play as the ceiling approaches, which splits the chance among more players.

Before you play one

• Read the rules for whether a minimum or maximum bet is needed to qualify for the top prize.
• Check how the jackpot is paid. Network jackpots are usually paid by the studio or network, sometimes in instalments on land-based machines.
• Compare the base-game RTP with a non-jackpot slot. The difference is the price of the jackpot ticket built into each spin.