How the calculator works
From the number of reviews and the percentage distribution, you get the number of reviews for each star rating. The average is the sum of all stars divided by the number of reviews. To offset one new 1-star review, you need (average − 1) ÷ (5 − average) new 5-star reviews, rounded up.
The calculation shows why bad reviews hit good products so hard: at 4.5 stars, it takes 7 new 5-star reviews to offset a single 1-star review. Removing one impermissible review often has a bigger effect than many new good ones.
Why the value on Amazon can differ
Amazon does not show a simple average. The star rating comes from a model that weights reviews, for example by their age and by whether it was a verified purchase. The calculator is therefore an approximation. It is accurate enough to show how much individual reviews matter.
Frequently asked questions
How many 5-star reviews offset one 1-star review?
That depends on the current average. Mathematically, it takes (average − 1) ÷ (5 − average) new 5-star reviews. At 4.0 stars that is 3, at 4.5 stars 7 and at 4.8 stars 19. The better the average, the more costly each single 1-star review becomes.
Does Amazon calculate the stars the same way?
Not quite. Amazon does not calculate the star rating as a simple average but with its own model that weights reviews differently, for example by age and by whether it was a verified purchase. The calculator shows the simple average as an approximation: the direction is right, but the exact value on Amazon can differ.
Where do I get the numbers?
On the product page under “Customer reviews”: it shows the number of reviews and the percentage for each star rating. It is faster with our free preview: enter the ASIN and you see the distribution right away.
Which reviews can be removed at all?
Only reviews that violate Amazon’s guidelines or applicable law. The guide Getting Amazon reviews removed explains which reviews these can be.