It might sound a little shocking considering the number of pretty reputable brands that built and market free google review calculators, but they are all unequivocally WRONG.
The rounding problem
Google rounds ratings up from 0.50 and down from 0.49.
This means if a business shows a rating of 4.7 stars on Google, their average rating could be anywhere between 4.650 and 4.749.
That's a huge range.
In the example below, I tested a few calculators on a small restaurant in Aix en Provence. They all gave the same result of 136 reviews required to move the rating.
The actual value was 35.
That's more than 3 times less.
An example to illustrate the problem
Let's take this Tapas restaurant in Sunny Provence as an example
At the time of writing, they have 145 reviews, and Google shows a rating of 4.9.
All calculators I've tried will tell you you need 136 5 star reviews to get to a 5.0 rating.
Here's two example
Which basically means 2X the current number, with 5 star reviews only.
Which essentially tells the business owner, don't bother.
Now we can debate whether having a rating of 5.0 is better or worse than 4.9, and there's certainly a lot more to deciding whether this should be a priority or not.
But in reality, that tapas restaurant has an average rating of 4.938.
Which means getting just 35 5-star reviews would get them to a 5.0 rating.
Not 135.
Just 35.
That's more than 3 times less that what other calculators returned.
The maths
Rc: current average rating (e.g., 4.47)
C: current review count (e.g., 200)
R₃₀d: expected average rating of new reviews (e.g., 5)
Rt: target rating you want to display (e.g., 4.8)
To display a rating of Rt, you need enough reviews for your "real" average to reach at least (Rt - 0.05) because Google rounds up at .50.
n: number of new reviews needed at average rating R₃₀d to reach the target display rating Rt
The real solution
The ONLY way to get an accurate estimate for the number of 5-star reviews you'd need to move your rating is to calculate the exact average rating of all your google reviews.
And to do that, you need to pull all your reviews from Google.
Sounds simple enough, and that's how we had initially built our very own google review calculator which was entirely free to use and play around with.
That was until Google decided we couldn't do that anymore.
The data problem
In February 2026, Google has made Google reviews unavailable to logged out users. This effectively means you can't scrape Google reviews anonymously now, and the review data isn't publicly available anymore. It's protected by a login wall.
This makes scraping reviews illegal, and extremely easy to detect (and block).
So now the only way to access all your Google reviews is to have you authenticate your Google Business Profile account, and to use Google's GMB API to access your reviews.
While you could technically offer this as a 100% free service, there are costs directly involved, and more importantly, it is not required to handle fairly sensitive customer credentials to access Google reviews.
This means you effectively mean to provide customers with secure accounts, which comes with all sorts of account management features, etc.
In my opinion it now makes more sense to provide a secure, reliable, and accurate calculator for customers that are willing to pay for this service. Anything else would be irresponsible.
Why the number of 5 star reviews you need isn't helpful
Getting 5 star-reviews only isn't realistic.
Especially if you haven't been getting 5 star-reviews only so far.
If you actually want to improve, and have actionable information, I recommend you look at your mobile 30 day average rating instead.
The mobile 30 or 7 day average is the average of the ratings of the reviews you collected over the past 30 days (or 7 days).
Compare that value with your overall rating.
If your mobile average is higher than your overall rating, you're improving.
If your mobile average is lower than your overall rating, your rating is effectively decreasing.
Your 30 day average is the best indication of how your review collection is performing right now. Don't count how many 5 star reviews you need.
A Google Review Calculator that actually works
On Reviewflowz, all subscribers can access a detailed calculator for all their registered Google business profiles from the Lite plan.
You can try this on a 14 day free trial. We do not require a credit card to start a trial.
It looks a little something like this
In this example, if everything continues the exact same way, our Kebab joint will see its rating increase to 3.9 in the next 3 days.
Now for the most interesting part.
If you scroll down a bit, you'll get a simple screen with 2 outputs, and 3 inputs:
Outputs
The number of new reviews required to get to your target rating (first input)
The number of days required to gather that many reviews (second input)
Inputs
The Target Rating: By default, current rating + 0.1 (next rating). You can play with this and increase it to your actual objective. Or on the contrary, use it to define an ambitious, but obtainable target.
New reviews per month: By default, the # of reviews collected over the past 30 days. You can play with this to see how review velocity (the # of reviews you collect per month) can get you to your target faster.
New reviews average rating: By default, the average rating of the reviews collected over the past 30 days. You can play with this to see how increasing your review rating can get you to your target faster.
It's generally safe to assume that if your review collection is too aggressive, you'll end up collecting "meh" reviews – which might hurt your average rating.
However if you're not being aggressive enough, you'll likely end up with a few 5 star reviews, and a few 1 star reviews from the occasional angry customer. Nobody can consistently provide a perfect experience.
The objective should be to experiment to figure out how aggressively you and your team should collect reviews to get to your target rating as early as possible.