A hundred and fifty pounds for a Saturday night sounds fine.

It sounds like money. It sounds better than nothing, which is what most of the other offers are. And it stays sounding fine right up until you write down the drive, the load-in, the hour of standing about, the soundcheck, the strings, the parking and the drive home.

Then it is £16.25 an hour, before tax, on a night you will not get back.

That is not an argument for turning the gig down. It is an argument for knowing the number.

What it counts

The fee. The round trip in miles, at whatever your real cost per mile is — the tool starts at HMRC's 45p because that is the number the taxman uses, but it is a field, not a law. The other costs: strings, parking, the service-station sandwich.

And then the part everybody leaves out: the hours.

Not the two hours on stage. The travel, the load-in, the soundcheck, the waiting. That is where a gig actually goes. A two-hour set is a six-hour night, and if you divide the fee by two you are not calculating a rate, you are telling yourself a story.

The verdicts

Below seven pounds an hour, it says so plainly: the venue could not legally pay a glass collector this. That is worth carrying into the next conversation with a promoter.

Between seven and fifteen is working-musician territory, and the tool asks the only question that matters there — the gigs are sustainable if they also feed something. Fans, sales, songs, joy. Do they?

And if the number comes out negative, it does not scold. Paying to play can be a completely valid choice. Exposure, the love of it, the hang, the fact that this particular room matters to you. The tool's only position is that it should be a choice rather than a surprise.

Why give it away

Because artists share numbers with each other far less than they should, and vaguely-remembered fees are how the whole ecosystem stays underpriced.

Also because I am on both sides of this. I make music and I build the software that connects musicians to gigs, and the second job is considerably easier to do honestly if I am not pretending about the first.

What it is not

It is not accounting. It ignores tax, it ignores gear depreciation beyond whatever you type into "other costs", and it certainly does not know about the amp you are still paying off.

It runs in your browser. Nothing is sent anywhere, which given that these are your actual earnings seemed like the only defensible way to build it.