17 free startup calculators — no signup required

Which calculator you need

If you are still deciding whether an idea is worth pursuing, start with market size and break-even. Together they answer the two questions that kill most ideas early: is the market big enough to matter, and how many customers do you need before the business sustains itself?

Once you have customers, the unit-economics calculators become the useful ones. CAC and LTV only mean something in relation to each other — a £900 acquisition cost is excellent against a £6,000 contract and fatal against £120 a year. If you are planning a raise, runway and equity dilution matter most.

The inputs that get fudged

Most of these calculations go wrong in the same predictable ways. Acquisition cost gets understated by counting only advertising and excluding salaries, often by a factor of two or three. Lifetime value gets inflated by using revenue instead of gross margin, and again by using a hoped-for churn rate rather than an observed one. Market size gets calculated top-down from a published industry figure, which is unfalsifiable and therefore discounted by anyone experienced.

Each calculator states what belongs in its inputs, and the glossary explains the underlying terms with worked examples. Nothing you enter is stored or transmitted — the maths runs entirely in your browser.