Free Spins Bonus Rounds Explained: Triggers, Tiers & Retriggers
By Scatter Drop Editorial Team · Updated 10 November 2026 · 2 min read
The free spins round is still the most common bonus in online slots. It's where most games keep the bulk of their winning potential – which is why understanding how a slot's bonus works matters more than almost anything else in its paytable.
How free spins trigger
The usual trigger is three or more scatter symbols in one spin. Variations include scatters that only land on certain reels, bonus symbols that must land on the same row, or meters that fill over several spins. Some games award extra spins for each additional scatter.
What makes free spins better than base spins
A bonus round is only exciting if something is improved compared to the base game. Common upgrades:
- Expanding symbols – a randomly chosen symbol expands to fill reels, as in Book of Dead and other book slots.
- Sticky or growing multipliers – multipliers that persist and climb through the round.
- More special symbols – higher odds of wilds, collectors or modifiers. Big Bass Bonanza adds fisherman collectors that only appear in the bonus.
- Guaranteed features – a modifier that is assured on every bonus spin.
Tiered bonuses
Hacksaw Gaming popularised the three-tier bonus: three scatters give the basic round, four give an upgraded version, and a special symbol unlocks the top tier. In Wanted Dead or a Wild and Chaos Crew, the upper tiers are rare but carry most of the game's max-win potential. Nolimit City uses the same idea – The Crypt has a standard and a more volatile bonus.
Retriggers
A retrigger awards more spins when scatters land during the bonus. Generous retriggers can turn a short round into a long one; some games cap the total number of spins.
Bonus buys
Many slots let you buy direct entry to the bonus for a fixed multiple of your stake, often 100x. A bonus buy does not improve your long-term return – it simply swaps many base-game spins for one expensive shortcut. Bonus buys are banned in Great Britain and some other markets. See bonus buy explained.
How often does the bonus trigger?
Far less often than most players expect. Across the BGaming games that publish it, the median bonus frequency is around 1 in 180 spins. Our guide to hit frequency explains how to use these numbers when you plan a session.
