SaaS runway: how to calculate it, with a calculator

The runway formula

Runway is how many months your business can keep operating with the cash it has, if nothing changes. For a bootstrapped SaaS, the useful version uses net burn, because your revenue is paying part of the bills:

Net burn = monthly expenses − monthly revenue

Runway (months) = cash available ÷ net burn

Cash available is money you can actually spend on the business: the business bank balance plus any payouts already on their way from your payment processor. Leave out money set aside for tax, personal savings you would never put in, and anything you are not sure you will collect.

If net burn is zero or negative, the formula stops making sense. That is good news: you are profitable and runway is effectively unlimited at current numbers. The burn rate guide goes deeper on gross versus net burn.

Runway calculator

Fill in your own numbers. The growth field is optional: set it to your typical monthly revenue growth and the calculator simulates month by month instead of assuming revenue stays flat.

Worked example

A founder with two small products has $24,000 in the business account. Over the last three months, revenue averaged $1,800 and expenses averaged $3,400 (hosting, tools, a part-time contractor and a modest salary).

The table is the point. Runway is rarely one number; it is a range, and seeing which lever moves it most tells you where to spend the next month. Here, cutting one cost more than doubles runway, while a $400 revenue loss shortens it by three months.

Making the inputs honest

Most runway mistakes come from optimistic inputs, not the arithmetic. A few rules help:

1. 1.Average the last three months of revenue and expenses rather than using your best month.
2. 2.Spread annual costs (domains, annual tool plans, insurance) across twelve months so the month they land in does not distort burn.
3. 3.Include what you pay yourself. If you are not taking a salary but need to eventually, model both.
4. 4.Record revenue net of refunds, and treat processor fees as an expense.
5. 5.Hold back cash reserved for tax. It is not runway.

Default alive or default dead

A useful framing: at your current growth rate and expenses, will revenue overtake costs before the money runs out? If yes, you are default alive. If no, you are default dead, and something has to change: costs, pricing, growth or funding. Try the growth field in the calculator above with a realistic number. Many small SaaS products are closer to break-even than the flat runway number suggests.

How much runway is enough?

There is no universal answer. Venture-backed startups often aim for 18 to 24 months after a round, because raising again takes time. A bootstrapped founder with low fixed costs may be comfortable with less, as long as it is not shrinking month after month. What matters more is the trend: runway that grows each month means the business is heading towards self-sufficiency, even if the absolute number is small.

Set a personal floor (for example, six months) and decide in advance what you will do when you hit it. Making that decision while you are calm is much easier than making it at two months.

Keeping it current

Runway is only useful if it is recent. Recalculate it as part of a monthly close: update cash, review recurring costs, check revenue per product. The monthly close checklist takes about thirty minutes. If you run several products, also check which one is driving the burn; the guide to tracking multiple SaaS projects shows how to split shared costs fairly.