The sum itself
No estimate, no industry benchmark, no weighting anyone invented. Your rating is a plain mean: add up every star and divide by the number of reviews. So the number of new reviews you need is fixed by three things, and you can check it on paper.
reviews needed = how many you have, times the gap you are closing, divided by how far a 5-star sits above your target
That last division is why the answer grows so fast as you approach 5. Moving from 4.3 to 4.5 means each new 5-star review buys you half a star of headroom. Moving from 4.3 to 4.9 leaves a tenth, so the same climb costs six times as many reviews.
Why your history is the weight
Two businesses both sit on 4.3 and both want 4.5. The one with 23 reviews needs 10 more. The one with 112 needs 45. Nothing about the second business is worse. It simply has more history holding the average where it is, and every review it ever collected is now pulling against the move.
This cuts both ways, and it is the most useful thing on the page. A long review history is slow to improve and almost impossible to damage. A short one moves fast in whichever direction it is pushed.
The rating people see
Google displays one decimal place and rounds to it. An average of 4.44 shows as 4.4. An average of 4.45 shows as 4.5. Everything in between is invisible.
That matters more than it sounds, because the number your customers judge you on moves in steps. Sit on 40 reviews at 4.44 and a single 5-star review takes your public rating from 4.4 to 4.5. Most calculators aim at the raw average and miss this entirely. The one above gives you both, because the cheap win is usually the visible one.
What you can ask for
Worth being clear, because the rules changed. Since 6 April 2025 the DMCC Act has made it a banned practice in the UK to write or commission fake reviews, or to offer an incentive for a positive review without disclosing it. The CMA can now fine businesses directly, up to £300,000 or 10% of global turnover, whichever is higher.
Still completely fine: asking every customer, every time, for an honest review. Putting the link on the invoice, the receipt, the thank-you email and the van. Replying to the ones you get.
Not fine: asking only the customers you think are happy, offering a discount for five stars, or writing them yourself. The line is not about asking. It is about filtering and paying. This is general information rather than legal advice, and the CMA publishes its own guidance if you want the detail.
Getting the number
Nearly every business that asks us about reviews is not short of happy customers. It is short of a habit. The ones who fix it do the same three things: they ask at the moment the job is finished rather than a week later, they make the link one tap rather than a search, and they ask every customer instead of the ones they feel confident about.
If the number above looks impossible, the target is usually wrong rather than the business. Going from 3.8 to 4.5 on six reviews takes nine. Going from 4.3 to 4.9 on 112 takes over a thousand. Pick the target you can reach this year.
