20+ years reviewing 10,000+ slots, breaking down games honestly to help you make smarter choices and have fun.
Reviewed and maintained by Chris Taylor - OLBG Slot Content Manager
Each OLBG slot review includes a modelled analysis of game behaviour during a typical playing session. This page details our methodology, the tool’s capabilities and limitations, and why our approach offers a clearer idea than relying solely on the published RTP percentage.
We provide full transparency so you understand how we calculate every figure we publish. If I cannot clearly explain a claim, I will not make it.
Why we built a slot simulator
Every online slot publishes a Return to Player (RTP) figure. For example, Preach TV lists 96.21% and Great Ghosts 96.5%. At first glance, these numbers suggest that wagering £100 would return about £96.
However, this interpretation is incorrect. The difference between perceived and actual meaning is a common misunderstanding in online slots.
RTP is a statistical limit, not a forecast. It represents the long-term average return over billions of spins, far beyond what any individual will play. While accurate and independently verified, RTP offers little guidance for short sessions, such as 100 spins.
Two games with a 96.5% RTP can deliver very different experiences. One may pay small amounts frequently, resulting in a gradual loss, while another may pay infrequently but in larger sums. Despite identical RTP figures, the actual gameplay can vary significantly.
This difference is due to volatility. Providers typically publish volatility as a single word such as "Medium" or "High." However, this describes only the general trend, not the degree of variation.
We developed the OLBG Slot Simulator to address this gap. It uses published game data to demonstrate what those figures mean during a typical session with standard stakes.
What the simulator is - and what it is not
We have placed this section near the top due to its importance.
What it is
The OLBG Slot Simulator is a mathematical model. It uses a game's published parameters-RTP, hit frequency, volatility rating, bonus trigger rate, and maximum win multiplier - to simulate sessions consistent with those values and reports the outcomes.
What it is not
It is not the actual game. The simulator does not connect to Preach TV, Great Ghosts, or any other slot, nor does it use the provider's random number generator, reel strips, symbol weightings, or pay table, as this information is not publicly available.
Slot providers do not publish their PAR sheets - the Probability Accounting Reports that contain the true reel layouts and symbol frequencies. Those documents are commercially confidential and shared only with regulators and licensees. Nobody outside a provider or a test house can replicate a specific slot's exact mathematics, and anyone claiming otherwise is not telling you the truth.
Instead, the simulator addresses a different and more practical question:
"A game with 96.21% RTP, 23.75% hit frequency and very high volatility - what does that combination of numbers actually feel like across 100 spins at £1?"
This question has a clear, evidence-based answer that the published RTP figure alone cannot provide.
The results illustrate the range of possible outcomes, not the result of any specific session. For example, if the simulator shows a session ending down £46, it indicates that sessions with those characteristics often fall within that range, which the headline RTP does not reveal.
The game data we use
Every simulation is anchored to the parameters published by the game's provider and shown on our review page for that slot:
RTP | Theoretical long-run return percentage | Provider / test house certified |
Hit frequency | Percentage of spins that return any win | Provider published figure |
Volatility | Payout distribution rating, 1–10 | Mapped from the provider's rating |
Bonus trigger rate | Average spins between bonus rounds | Provider published, where available |
Max win | Maximum possible win as a multiple of stake | Provider published figure |
If a provider's published figures are inaccurate or measured on a different basis, our model inherits that inaccuracy. We are dependent on the same source data as every other reviewer. The difference is what we do with it.
How the model works
The pay table
Actual slots do not pay out evenly. Most spins result in no payout, small wins occur frequently, and large wins are extremely rare.
Our model uses a weighted pay table with thirteen tiers, ranging from 0.2× to 1,500× the stake. Approximately 45% of winning spins return less than the original stake, which is fundamental to slot mechanics. For example, in the popular slot Starburst, it is common for a winning combination to pay out only £0.40 or £0.50 on a £1 spin, illustrating that even when a spin is technically a "win," the player still experiences a net loss.
The pay table’s structure is determined by volatility. Low volatility games concentrate probability in small, frequent wins, while high volatility games shift probability toward rare, larger wins, resulting in longer losing streaks and occasional significant payouts.
Session variance: why we use a gamma distribution
This approach ensures our model more accurately reflects real-world outcomes compared to a basic simulation.
A common approach is to model session variance with a normal distribution centred on the RTP. However, this is inaccurate, as it assumes symmetry in outcomes, which does not reflect actual slot behaviour.
Actual slot sessions are right-skewed. Most sessions end below the average due to the house edge and the rarity of large payouts. Only a few sessions achieve significantly higher returns, which raises the long-term average to the published RTP.
Therefore, we use a gamma distribution to model session returns, as it naturally produces this skewed shape. The distribution’s shape parameter is determined by volatility:
- Low volatility produces a shape parameter around 4.0 - results cluster fairly tightly around the mean, mild skew.
- Very high volatility produces a shape parameter around 0.85 - heavy skew, most sessions well below the mean, rare sessions dramatically above it.
This explains why our results consistently indicate that most sessions end in losses for high-volatility games. For players, this means that while the potential for large wins exists, the typical experience is characterised by frequent losses, which is an inherent feature of high-volatility slot design.
Reinvestment: why your money is worth less than the RTP suggests
This point is often overlooked but is crucial to understanding slot outcomes.
When you win on a slot, the winnings are added to your balance and typically wagered again. The house edge applies to each subsequent wager.
The published RTP applies to each pound wagered. However, your initial £100 is wagered multiple times as you reinvest winnings, resulting in a total wagered amount that exceeds your starting balance.
If you play until your balance is depleted, you will lose your entire original stake regardless of RTP. A higher RTP only extends the duration of play, not the outcome.
For fixed-length sessions, the effect is less pronounced but remains significant. Our simulator calculates a reinvestment-adjusted effective RTP, which represents the actual return a player is likely to experience after accounting for the fact that winnings are typically reinvested during play and thus subject to the house edge multiple times. This adjusted RTP is shown alongside the headline figure as an approximation that more accurately reflects typical player behaviour.
The key takeaway is direction, not precision: your actual returns are lower than the headline RTP suggests. Reviews quoting RTP without this context can be misleading. Bonus rounds
In most modern slots, the bonus round provides the primary opportunity for significant wins, while base game spins typically reduce the balance.
Our model uses a separate seventeen-tier distribution for bonuses, weighted to reflect actual bonus round outcomes rather than player perceptions:
Dud | ~30% | 2–8× stake |
Low to mid | ~45% | 8–25× stake |
Decent | ~18% | 25–80× stake |
Big | ~6% | 80–300× stake |
Mega | ~1% | 300×+ stake |
The distribution is weighted toward lower returns. Approximately 75% of bonus rounds pay less than 25× the stake, which often does not cover the cost of reaching the bonus. This reflects the true nature of bonus-dependent slots, contrary to industry marketing.
Our simulator displays the distribution of bonus outcomes across test runs, allowing you to see the frequency of both low and high results.
Two further refinements
Path dependency: When a session’s balance drops below 40% of the starting amount, our model slightly increases the hit rate to reflect the tendency for players to chase losses. This adjustment produces more realistic balance fluctuations.
Minimum hit floor: Our model prevents statistically improbable results. For example, if a simulation produces fewer than a quarter of the expected hits, the model corrects it to avoid unrealistic outcomes.
Our standard test
For every slot review, we run a standard test:
- 5 sessions
- 100 spins per session
- £1.00 per spin
- £100 starting balance per session
- 500 total simulated spins
We selected these figures to reflect typical player behaviour. One hundred spins at £1 mirrors a realistic session for a £100 budget. Running five sessions demonstrates the range of possible outcomes.
Longer simulations are available and serve a different purpose. As spin count increases, returns converge toward the published RTP, validating the model. However, shorter runs better represent typical player experiences.
Reading the results
Avg observed RTP | Mean return across the test sessions |
RTP range | The spread between best and worst session - the volatility made visible |
Sessions ending in loss | How often a session of this length loses money. On a high-volatility game this is usually the majority |
Effective RTP | Return on original cash after reinvestment drag |
Avg bonus payout | What bonus rounds actually delivered, in multiples of stake |
Balance trajectory | The shape of the session - where the money went and when |
We recommend focusing first on the percentage of sessions ending in loss because this metric provides a clearer representation of the typical player experience. While it is often omitted by the industry, emphasising the loss percentage enables players to understand better the likelihood of not achieving a profit in a typical session, thereby offering a more realistic perspective on expected outcomes than aggregate metrics such as RTP.
Limitations - stated plainly
We want to be transparent about the following limitations:
- This is a model, not the game. It does not use the provider's actual RNG, reel strips or pay table, and it cannot.
- Our pay table is an archetype. It is shaped to be consistent with the game's published RTP, hit frequency and volatility - but it is not that game's specific pay table.
- Bonus distributions are approximations. They are modelled on noted patterns across many games, not on any individual game's bonus mathematics.
- Results generated by the simulator are illustrative rather than predictive, meaning that individual simulated sessions cannot forecast the outcome of any actual gameplay instance. Instead, the utility of the simulator lies in its ability to represent the broader distribution of possible outcomes across many sessions. This distinction has practical implications: players and analysts should use the results to understand the range and likelihood of different experiences rather than to anticipate precise results for a single session. Therefore, reliance on any single simulated result is inappropriate when evaluating potential gameplay, as it does not account for the inherent variability and chance that characterise real slot sessions.
- We inherit the provider's figures. If a published RTP or hit frequency is wrong, our output is wrong in the same direction.
- The reinvestment adjustment is a heuristic. Real reinvestment drag depends on session length, stake and when a player stops. We model a typical case.
These limitations do not affect our main point. While the published RTP provides a single long-term figure, our model offers insight into the distribution, likely outcomes, and the true impact of bonus rounds. Our goal is to present this information transparently.
Where this sits in our review process
The simulator is one component of our slot reviews. Our reviewers also assess gameplay, interface, features, mobile performance, and bonus mechanics. The simulator provides a reproducible, data-driven analysis that informs our conclusions.
Each review with simulated results lists the parameters used. Results are reproducible, and the tool is available for you to run your own simulations with custom settings.
Further reading
- Understanding slot volatility
- High volatility slots explained.
- Low volatility slots explained.
- Best payout slots and RTP explained.
- Try the simulator on any demo slot.
Responsible gambling
Nothing on this page, nor any simulator output, should be considered a strategy, prediction, or encouragement to play. Our modelling clearly shows that most sessions result in losses, which is inherent to how these games operate and how the industry is funded.
Gambling should be entertainment, and never money you cannot afford to lose. If you are worried about your own gambling or someone else's, free confidential support is available 24/7 from GamCare (gamcare.org.uk · 0808 8020 133) and GambleAware (gambleaware.org). You must be 18 or over to gamble in the UK.
