Not an estimate — the arithmetic is exact. And it will tell you when the target is mathematically unreachable at your current review quality, which is the answer most tools quietly avoid giving.
To lift your mean from where it is to a target t by adding n reviews that average r:
Where yourTotal = yourRating × yourCount. We target the competitor's rating plus 0.1, so you land clearly ahead rather than tied.
Notice the denominator: r − t. If the reviews you are adding average the same as, or less than, your target, that term is zero or negative and no value of n works.
Plainly: you cannot reach a 4.9 average by adding 4.5-star reviews. The tool says so instead of returning a number. That is the single most useful thing it can tell a business whose real problem is service quality, not marketing.
Passing their average and passing their volume are different problems with different answers. A competitor at 4.9 with 12 reviews is easy to out-volume and hard to out-rate; one at 4.4 with 400 is the reverse. We compute both and tell you which is binding.
Reviews are one input to local ranking, alongside proximity to the searcher and relevance. No number of reviews overcomes being five miles further away for a "near me" search. Treat this as sizing one lever, not as a ranking prediction — and be sceptical of anyone who tells you reviews alone will win the map pack.
Use the number as a target, not a promise: ask real customers for reviews, the same way every time, with no incentives. Consistent business details help local visibility too, so run the NAP Consistency Checker, and see what a stronger customer base is worth with the LTV:CAC Calculator. For local AI-search visibility, see our AEO and GEO consulting.