The short answer: Google adds up the star value of every published review and divides by the number of reviews, then rounds the result to one decimal place. There is no recency weighting, no Bayesian smoothing, and no secret sauce — it is a plain arithmetic mean. Everything that feels mysterious about your rating comes from two things: the rounding, and the size of the denominator.
The formula
Rating = (5×five-star + 4×four-star + 3×three-star + 2×two-star + 1×one-star) ÷ total reviews
So a business with 70 five-star and 30 four-star reviews has (70×5) + (30×4) = 470 points across 100 reviews, giving a true average of 4.70. Google displays "4.7".
That much is straightforward. What trips people up is what happens next.
The rounding rule almost nobody knows
Google shows one decimal place, and it rounds to get there. This means the number on your profile is not your rating — it is your rating rounded. To display 4.8, your true average only has to reach 4.75.
| To display | Your true average must reach | At 4.74, Google shows |
|---|---|---|
| 4.5 | 4.45 | 4.4 |
| 4.6 | 4.55 | 4.5 |
| 4.7 | 4.65 | 4.6 |
| 4.8 | 4.75 | 4.7 |
| 4.9 | 4.85 | 4.8 |
| 5.0 | 4.95 | 4.9 |
The consequence is that two businesses both showing "4.7" can be in wildly different positions. One might sit at a true 4.651, barely scraping into the band. The other might sit at 4.749 — a single review away from flipping to 4.8. The displayed rating hides this completely, which is why "my rating won't budge" and "my rating jumped overnight" are both common experiences.
You cannot tell where in the band you sit from your rating alone. You need your per-star breakdown — the actual count of 1, 2, 3, 4 and 5-star reviews.
Why one bad review devastates a new business and barely scratches an old one
Your rating is an average, so the damage a single review does is inversely proportional to how many reviews you already have. Here is exactly what one new 1-star review does to a business sitting at 4.8:
| Total reviews | Rating before | After one 1-star review | Damage |
|---|---|---|---|
| 10 | 4.8 | 4.5 | −0.3 |
| 25 | 4.8 | 4.7 | −0.1 |
| 50 | 4.8 | 4.7 | −0.1 |
| 100 | 4.8 | 4.8 | no visible change |
| 250 | 4.8 | 4.8 | no visible change |
| 500 | 4.8 | 4.8 | no visible change |
At 10 reviews, one angry customer costs you three tenths of a star and drops you out of the "excellent" band entirely. At 250 reviews, the same customer does not move your displayed rating at all.
This is the strongest practical argument for review volume. Reviews are not just social proof — they are insulation. A large review base means a bad week cannot wreck your profile, and it is the single best defence against a malicious or unfair review you cannot get removed.
It cuts both ways, of course. The same maths that protects an established business from a bad review also makes it enormously expensive for that business to improve — see how many 5-star reviews you need to increase your rating for the full cost table.
What Google does not do
- It does not weight recent reviews more heavily. A 1-star review from four years ago counts exactly as much as one from this morning.
- It does not use a Bayesian average. Some platforms pull low-volume businesses toward a global mean to stop a single 5-star review producing a perfect score. Google does not; a business with one 5-star review displays 5.0.
- It does not round to half-stars. The visible star graphic may be drawn in halves, but the number itself is to one decimal.
What Google does do is filter. Reviews that violate its policies — spam, conflicts of interest, off-topic content — can be removed, and removed reviews stop counting. That is why your review count sometimes falls, and why your rating occasionally moves when no new review has arrived. If reviews of yours have vanished, see why your Google reviews are missing.
Work out your own number
Because the displayed rating hides where you sit inside the band, the only way to know your true position is to work from your per-star breakdown.
The free Google Review Score Calculator pulls your live 1–5 star counts from Google, computes your exact unrounded average, and shows precisely how many 5-star reviews stand between you and each remaining milestone. It takes about five seconds and needs no signup.
Related reading
- How many 5-star reviews do you need to increase your rating? — the full cost table.
- Why did my Google rating drop? — the same arithmetic, working against you.
- How to get more Google reviews — earning the reviews the maths demands.