Google review calculator

How the calculation works

Your rating is an average: total stars divided by the number of reviews. If every new review is five stars, the average reaches the target when (rating × N + 5 × n) / (N + n) hits it. Solving for n gives n = (target × N − rating × N) / (5 − target), rounded up.

Example: with 120 reviews at exactly 4.2, you need (4.5 × 120 − 4.2 × 120) / 0.5 = 72 five-star reviews to reach 4.5. If the displayed 4.2 hides a 4.15 average, you need 84: that's the figure the tool shows first.

• Target already reached: if your displayed rating is at or above the target, you need no more reviews.
• A 5.0 target: impossible once any existing review is below five stars, because the exact average can never get back to 5.
• No reviews yet: one five-star review is enough to show 5.0.

Google's rounding: why a range

Google shows the rating to one decimal. A 4.2 means a real average between 4.15 and just under 4.25: you don't know it to the hundredth. So the tool gives two bounds:

• the worst case, shown large: the real average is as low as possible, and the target must be reached without relying on rounding;
• the best case: the real average is as high as possible, and the target shows as soon as rounding displays it.

The calculation assumes every new review is five stars. Each review of four stars or fewer pushes the target further away, so allow a margin. Google doesn't publish the details of its calculation; a simple average is the best approximation available.

What a 1-star review costs

Once you hit your target, a 1-star review pulls it down. To get back to the same average, you need (target − 1) / (5 − target) five-star reviews, rounded up, whatever your review count: 3 at 4.0, 5 at 4.3, 7 at 4.5 and 19 at 4.8. The higher you aim, the more each negative review counts, which is why it pays to respond well to negative reviews.

Your review count matters too: with 20 reviews, a single 1-star review can cost two tenths; with 500, it barely moves the displayed rating.

Getting those reviews, by the rules

Google recommends asking customers for reviews with a link or QR code (Google help). Its policy prohibits offering incentives (payment, discounts, free goods or services) and asking only happy customers, known as review gating (Google Maps policy). Send the same link to everyone.

• Generate your Google review link and QR code to send after each visit.
• Print a review sign, counter stand or stickers for your counter or tables.
• The guide to getting more Google reviews covers the right moment and channels.

Google lists reviews among local visibility signals, alongside relevance, distance and prominence (Google help on local ranking). A higher rating doesn't guarantee a higher position, but it weighs on customers who compare.