Bonus features are where a slot's personality really comes through. While the base game establishes the mechanical foundation, the bonus round is usually where the theme, drama and biggest potential wins are concentrated. Here's how the most common formats work.
Free spins rounds
The most widespread bonus format is a free spins round: landing a set number of scatter symbols (commonly three or more, depending on the game) during the base game triggers a fixed or variable number of spins that don't consume the player's balance. Free spins rounds frequently apply extra rules not present in the base game — added wild symbols, guaranteed multipliers, or a different symbol distribution altogether.
Wolf Gold's free spins round, for instance, adds extra wild symbols to the reels for the duration of the feature, while Starlight Princess and Gates of Olympus apply an accumulating multiplier trail that increases the value of golden multiplier symbols across the free spins session.
Multiplier symbols and accumulation
A multiplier symbol increases the value of a win by a stated factor when it appears as part of, or alongside, a winning combination. In cluster-pays and scatter-pays games, multiplier symbols are often a distinct, separate symbol type carrying its own randomly assigned value (for example, 2x, 5x, 25x, or higher), rather than simply doubling every win outright.
Some games — notably the Gates of Olympus and Starlight Princess families — feature multiplier accumulation during free spins, where every multiplier symbol landed during the round is added to a running total, and that combined total is applied to the final win at the end of the feature. This is a major reason these titles can produce very large multipliers relative to a single spin, and is closely tied to their high volatility rating.
"Money collect" and value-symbol features
A different bonus format, popularised by titles like Big Bass Bonanza and its sequel Big Bass Splash, uses cash-value symbols that land during a free spins round; the player collects the sum of every value symbol that appears, and landing a further special symbol (in Big Bass Bonanza's case, tied to the fishing theme) typically extends the round with additional spins. This format has become widely imitated across the industry because it gives players a running, visible tally of their potential win as the feature progresses.
Wild symbol variations
Beyond the standard "substitutes for any symbol" wild, many games add variations: expanding wilds that grow to fill an entire reel or row, sticky wilds that remain in place for multiple spins, or wilds that carry their own multiplier value. Which variation a game uses is part of what gives it a distinct identity even within a familiar theme.
Buy-in / bonus purchase features
Some providers, including Pragmatic Play on several of the titles covered on this site, offer a "buy feature" option that lets a player pay a set multiple of their stake to trigger the free spins round immediately, rather than relying on scatters landing naturally. This does not change the underlying odds or mechanics of the feature itself once triggered — it only changes how the round is accessed. Availability of buy-in features can vary by platform and jurisdiction due to regulatory restrictions.
Ante bet / enhanced-chance options
A related but distinct mechanic, sometimes offered alongside buy-in features, lets a player increase their base stake by a set percentage in exchange for an improved chance of triggering the bonus round on any given spin, without guaranteeing it outright. As with buy-in features, availability depends on the platform and jurisdiction.
How to read a bonus feature description
When we describe a bonus feature on one of our slot pages, we aim to specify: what triggers it, what changes about the game during the feature (extra wilds, multiplier accumulation, a different symbol set), and whether it can be retriggered or extended. This structure should make it possible to compare bonus rounds across different games on this site even when their themes are completely unrelated.
Bonus features don't change the odds
A more dramatic-looking or more generous-feeling bonus feature does not mean a game is more likely to pay out overall. All bonus mechanics are already accounted for within a game's published RTP and volatility figures — see our RTP guide for context.