Every progressive jackpot meter is a running total of other people's spins. That sounds blunt, and I mean it to, because once you read the number that way most of the mystery falls away. A slice of every stake goes into a shared pot, the pot climbs until one spin somewhere triggers it, and then it drops back to a starting figure and begins again.
I have watched these meters tick over for years, in seaside arcades and on online slots, and the mechanics have barely changed. The interesting part is the detail: how many games feed the pot, how much of your bet goes into it, what it resets to, and whether it is allowed to climb forever or has to drop by a deadline.
Where the money in a progressive jackpot comes from
A fixed jackpot is a set prize printed on the paytable, for example 5,000 times your stake for five of the top symbol. A progressive jackpot has no fixed value. The game sets aside a percentage of each qualifying bet and adds it to the jackpot meter. Picture a game that diverts, say, 2p from every £1 spin. One spin moves the meter by 2p. Ten thousand spins move it by £200.
That contribution comes out of the game's return to player. If a progressive slot lists an RTP of 96%, part of that 96% is the jackpot share, so the base game, meaning the ordinary line wins and free spins, pays back less than the headline figure. Almost nobody ever collects the jackpot share, which means a normal session on a progressive runs on a thinner return than a non-jackpot slot with the same printed RTP. I explain how that headline percentage is worked out in what RTP and volatility really mean, and progressives are the clearest case of the figure hiding more than it shows.
The pot getting bigger does not make it easier to win.
The chance of triggering the jackpot on a given spin is set by the game's maths and the random number generator. It is the same whether the meter reads £20,000 or £12 million. A big number only changes how much you would get, never how likely you are to get it.
Standalone, local and wide-area progressives
Progressives come in three broad sizes, and the size of the pool decides how fast the meter moves and how high it can go.
- Standalone. One machine, or one game, feeds its own jackpot. Only bets on that game count, so the pot grows slowly and tends to stay modest.
- Local or in-house. A group of machines in one venue, or a set of games at a single online casino, share a pool. In a land-based casino this is the row of identical cabinets under one big illuminated total.
- Wide-area or networked. Machines across many venues, or one game offered by many different online casinos, all feed a single jackpot. This is where the eight-figure numbers come from.
Networked jackpots are older than online casinos. IGT launched Megabucks in Nevada in March 1986, and it is usually described as the first wide-area linked progressive slot system: machines in different casinos across the state fed one jackpot, which started at $1 million. The base was raised to $7 million and then, in September 2005, to $10 million. Online, Microgaming's Mega Moolah plays the same part, one jackpot shared by every casino that runs the game, so a player in Leeds and a player on the other side of Europe are feeding the same pot. If you want the earlier history, my short history of the slot machine covers the road from the Liberty Bell to linked cabinets.
| Type | Who feeds the pot | How fast it grows | Typical top prize |
|---|---|---|---|
| Standalone | One machine or one game | Slowly | Usually the smallest of the three |
| Local | One venue or one casino's games | Steadily | Larger, still bounded by one site's traffic |
| Wide-area | Many venues or many casinos | Quickly | Can reach millions |
Seed amounts, contribution and the reset
When a progressive pays out, it does not fall to zero. It resets to a seed, a guaranteed starting value put up by the operator or the game supplier. Megabucks resets to its base figure, and online networks do the same with their own seeds. A jackpot that started from nothing would take weeks to look worth chasing, so the seed is as much a marketing decision as a mathematical one.
Many games split each contribution in two. Most of it tops up the jackpot you can see, and a smaller part goes into a hidden reserve that will pay for the next seed, so the reset is already funded on the day somebody wins. Games with several tiers run this process for every pot at once. Mega Moolah, for example, has four, named Mini, Minor, Major and Mega, each with its own starting value and its own growth rate.
The contribution rate tells you more about a game than the meter does: a high contribution means a fat jackpot and a leaner base game. The exact percentage is rarely advertised, but the help screen should explain how the jackpot is triggered and whether every stake qualifies.
Must-drop jackpots work differently
A classic progressive has no ceiling and no deadline. It can sit unclaimed for months. A must-drop jackpot is built the other way round: it has a maximum, or a time, by which it is guaranteed to pay. Red Tiger built a network around the idea in 2019. Its Daily Drop jackpot is guaranteed to pay out every day, and later that year the company added hourly jackpots on top. The largest daily prize reported in coverage from that summer was £61,500, landed from a £2 stake on Dragon's Luck in July 2019.
This is the one kind of jackpot where the meter does tell you something. As a must-drop pot nears its limit, the chance that it lands on one of the next few spins really does rise, because the game has to pay it before the cap. What does not rise much is your own share of that chance, because hundreds of other players are looking at the same meter and spinning at the same moment. A standard progressive, on the other hand, is never "due". A pot that has not paid for six months is exactly as likely to pay on the next spin as one that paid yesterday, the same mistake I write about in the night the Monte Carlo wheel hit black 26 times.
The record wins, and one odd footnote
The biggest slot jackpot on record came from a land-based network. On 21 March 2003 a 25-year-old software engineer from Los Angeles, who chose to stay anonymous, hit Megabucks at the Excalibur in Las Vegas for $39.7 million, having put roughly $100 into the machine. The odds of hitting the Megabucks top prize are widely put at around 1 in 50 million.
Online, Guinness World Records lists Jon Heywood from the UK as the winner of the largest online slot jackpot at the time it was ratified: €17,879,645, about £13.2 million, on Mega Moolah at Betway on 6 October 2015. That figure has since been beaten on the same network. In April 2021 a Belgian player at Napoleon Sports & Casino won about €19.4 million on Absolootly Mad: Mega Moolah, reported as the largest jackpot the Mega Moolah network had paid.
The footnote is Elmer Sherwin, a Las Vegas resident and Second World War veteran. He hit Megabucks for $4.6 million at The Mirage on 22 November 1989, the casino's opening night, and that one win started the long-running myth that Megabucks pays out when a new casino opens. Casino.org later counted 47 Las Vegas openings since without an opening-night Megabucks hit. Sherwin did win again, though: $21.1 million at the Cannery on 15 September 2005, at the age of 92. What people do once a sum like that lands is a different story, and I collected a few of the stranger ones in the craziest things people have done after winning a jackpot.
Progressive slots in the UK
Online progressives offered to players in Great Britain have to run at casinos licensed by the Gambling Commission, and you have to be 18 or over to play. Since 2025 they also fall under the online slots stake limits: £5 per spin for adults aged 25 and over from 9 April 2025, and £2 per spin for 18 to 24 year olds from 21 May 2025. Those caps cover slots only, not roulette or blackjack. For a progressive the cap matters more than you might think, because on games where a bigger stake buys a bigger chance at the jackpot, the ceiling on that chance is now set in law.
Frequently asked questions
Does a progressive jackpot get easier to win as it grows?
No. The chance of triggering a standard progressive on any single spin is fixed by the game's maths and does not change with the size of the pot. Only must-drop jackpots, which are guaranteed to pay before a set limit or time, become more likely to land as they approach that limit.
What is a seed amount on a progressive jackpot?
The seed is the guaranteed value the jackpot resets to after it is won. It is funded by the operator or the game supplier, often from a reserve built up out of earlier contributions, so the pot never restarts at zero.
What is the difference between a local and a wide-area progressive?
A local progressive pools bets from machines in one venue, or games at one online casino. A wide-area progressive links machines or casinos across many sites into a single pot, which is why networked games such as Megabucks and Mega Moolah reach far bigger totals.
Do the UK stake limits apply to jackpot slots?
Yes. The Gambling Commission's online slots stake limits cover progressive slots like any other online slot: £5 per spin for players aged 25 and over, and £2 per spin for players aged 18 to 24.