(4.5 × 107 − 444.5) ÷ (5 − 4.5), rounded up = 74
Add 7 hypothetical reviews at 3.5 stars to the raw inputs: (420 + 7 × 3.5) ÷ (100 + 7). This calculation uses effective totals that include the fixed prior. Start with 444.5 star points across 107 reviews. Each new five-star review adds 5 points and one review. Solve for an average of at least 4.5, then round up to a whole review.
Two questions. One calculator.
Enter exact star counts or an estimated average and total. Choose a target to find the minimum number of additional five-star reviews, including the difference between actual and displayed ratings.
With 100 reviews averaging 4.2 and a prior of 7 hypothetical reviews at 3.5, the estimate is (420 + 24.5) ÷ 107 ≈ 4.154.
New five-star reviews = ceil((target × (reviews + prior weight) − (star points + prior weight × prior rating)) ÷ (5 − target))
Reaching an actual 4.5 takes 74 new five-star reviews with this fixed prior. The 7 hypothetical reviews are excluded from the real review count.
Add ten five-star and three one-star reviews to the same starting data. Keeping the prior fixed gives (473 + 24.5) ÷ (113 + 7) ≈ 4.146.
Projected estimate = (existing star points + new star points + prior weight × prior rating) ÷ (real review total + prior weight)
This model does not reproduce age weighting, moderation or other unpublished platform rules.
Compare all rating methods. Within this calculator, choose a target or simulate how new reviews change your rating.
Google Maps describes its score as the average of published ratings. Arithmetic mean models that calculation; displayed rounding here is an assumption.
Trustpilot includes a prior of seven reviews at 3.5 stars and also considers review age. Our Bayesian estimate models a fixed prior only, so it is not an exact TrustScore calculator.
Amazon considers recency and purchase verification. IMDb uses undisclosed weights on a 1–10 scale. Their full ratings cannot be reconstructed from five star-count totals.
Bayesian rating = (raw star points + prior weight × prior rating) ÷ (real reviews + prior weight). Both methods support targets and simulated reviews. We do not connect to these platforms.
An exact 5 is impossible if any existing review is below five stars. A displayed 5.0 can be reached at an average of 4.95 under conventional one-decimal rounding.
The link contains the starting numbers and selected target or scenario. Anyone with the link can view the calculation. Editing it creates a different link; the original stays unchanged. Links contain numbers, not business names or review text.
Editing happens in your browser. Opening a calculation page sends the numbers in its URL to our server to render the result. We do not store calculations in a database. Bookmark or copy the link to keep a calculation.
{{detail}}
{{methodNote}}
{{/methodNote}} {{#recovery}}{{recovery}}
{{/recovery}}{{#estimated}}Estimate based on your entered average. {{/estimated}}Displayed rating assumes rounding to one decimal; platforms may use different rules.
Compare weighted averages, time decay, recent reviews, positive percentages, Wilson scores, medians and trimmed means. Each model explains its assumptions and can differ from actual service ratings.