How much runway do you need to start a business?

Six months of runway is the common pitch and usually the wrong answer. Most startups need 18-24 months because revenue ramps slower than founders expect. We model both costs and personal burn.

How the math works

Runway = cash ÷ monthly net burn. Net burn = monthly expenses − monthly revenue. Sounds simple; gets wrong because both sides change over time.

We model expenses as a piecewise function with planned hires, scaling infrastructure costs, and one-time legal/compliance bills. Revenue is modeled with conservative ramp assumptions: the calculator defaults to 60% of your projected ramp with a 2-month delay.

Three scenarios run automatically:

Base case: revenue ramp + planned hires + budgeted costs. Usually 14-18 months.
Revenue miss: 50% of projected revenue, otherwise unchanged. Usually 9-12 months.
Black swan: 50% revenue miss + 30% cost overrun + one-time legal/regulatory bill. Usually 5-8 months.

The fundraising adjustment: raising the next round takes 4-6 months from first meeting to wire transfer. Plus 2-month buffer for deals that fall through. Effective floor for fundraising start: 6-8 months of runway remaining.

Math runs locally. Inputs never leave your browser. Source on github.