Cash runway calculator: how many months you actually have

The runway figure most companies quote is cash divided by last month’s burn. One division, assuming every month from here looks exactly like the one behind you until the money is gone. The tool above reports that number beside a sixty-month projection in which revenue compounds growth against churn and the cost base drifts upward. The distance between the two is the point of this page.

What the calculator runs

The calculator has no arithmetic of its own. It hands your seven inputs to the same sixty-month engine the full simulator uses and reads the result. Each month, recurring revenue moves by growth minus churn, gross profit is revenue multiplied by margin, the cost base is re-indexed for inflation, and the difference lands in the cash balance. Runway is the last month before that balance goes below zero.

On the inputs as loaded — $750,000 in the bank, $120,000 of MRR, $160,000 a month of cost, 78% gross margin, 4.0% growth against 2.8% churn — the flat estimate is 11 mo, from $65,723 of net burn in month one. The projection gives 1y. They nearly agree here, which is luck rather than reliability: nothing in the flat number responds to the inputs that decide burn.

The other two tiles matter more than either. Break-even arrives at Month 59, the first month gross profit covers the cost base, and the lowest balance across the horizon is -$1.5M in month 58 — the size of the hole this plan digs if nobody funds it.

The assumptions, stated

A calculator that quietly reshapes your inputs is worse than none. Here is what happens to yours.

• One cost line carries everything. The engine’s separate channels for payroll, contractors, cloud and licences are all set to zero, so the single monthly operating cost you type is the entire cost base. Nothing is added behind it.
• That cost travels through payroll, not infrastructure. The obvious carrier, the fixed cloud-spend field, is the wrong one: the engine clamps it at $100,000 a month. Your cost becomes headcount at the $400,000 salary ceiling instead, left fractional, so $160,000 a month is 4.8 notional heads: a unit of cost, not a staffing plan.
• Cost inflation indexes the whole base. Because the base rides on payroll, your inflation figure is applied as salary drift too, so one rate governs all of it. At 3.4% the default base runs $160,446 in month one and $189,114 in month sixty — 17.9% more, for an identical business.
• Re-investment is zero. The full simulator can route operating profit into paid acquisition. Here it does not, so the growth rate you type is the growth you get and profitable months add cash rather than buying revenue.
• The horizon is fixed at sixty months, and nothing tops the balance up. A business that survives to month sixty is reported as never running out, which means only that it lasted five years.

Why burn never stays flat

Three things move burn, and the flat formula is blind to all three.

Revenue compounds. Growth and churn are not added once; they are applied to a base that changed last month. The net monthly rate is growth − churn, compounded, so 4.0% against 2.8% grows, while 1.0% against 6.0% halves the business in under a year. Burn narrows in the first case and widens in the second, from month two onward.

Costs drift. Salaries, tooling and vendor contracts do not hold their price. The drift is trivial monthly and not trivial over a plan: the default cost base ends the horizon 17.9% above where it started without a single hire.

Gross margin decides how much revenue arrives. Only gross profit reaches the cost base, so ten points of margin is ten points of every future month.

At 60% margin this company gets 8 mo and never covers its costs. At 95% it gets 1y 9mo and breaks even in month 38. Nothing else changed. Getting the cost-of-revenue classification right is worth more than most cost-cutting: SaaS gross margin explained.

Where the two numbers part

Which direction the gap runs depends on whether growth net of churn is beating cost inflation. Take a company with $1,000,000 in the bank, $200,000 a month of cost and 8.0% growth against 2.0% churn. Cash divided by this month’s burn is 10 mo — a number that gets a board meeting moved forward. The projection says it never runs out: the balance bottoms out at $222.1K in month 13 and recovers, because break-even arrives in month 14. The task is to survive the trough, not to raise against a fictional zero.

Now reverse it. A company with $3,000,000 — four times the default case — growing 1.0% a month against 6.0% churn, with cost inflation at 6.0%. The flat estimate promises 3y 6mo; the projection gives 2y 1mo, and the business never breaks even. Revenue falls 5.0% a month while the cost base climbs, so the burn behind that flat estimate is the smallest burn this company will ever have.

Churn, one point at a time

The growth-led company above is only growth-led while churn behaves. Hold every other input, move churn a point at a time, and watch which column responds.

Read the flat column first. It barely moves, because month one is nearly identical whatever churn is doing — one point of it is a rounding error against a $200,000 cost base for a single month. The projected column crosses from never running out to running out inside a year over the same range. The flat formula is not a rough version of the projection; it measures something else.

The middle rows are the ones to sit with. At 5.0% and 6.0% churn the projected runway is identical, while the trough falls from -$693.5K to -$1.7M and break-even slides from month 29 to month 45. Same runway, and one of them needs 2.5 times the cheque.

Plan around the trough, not the runway

Runway answers the wrong question. The number to plan around is the lowest cash balance and the month it happens, because that is the capital the plan actually consumes.

For the growth-led company the trough is $222.1K in month 13 — 22% of the opening balance, and the whole margin for error. Halve the growth rate to 4.0% and the same company runs out in 10 mo with a $1.7M deficit. Plans break at the trough.

Where the trough is negative, it is the raise. The default inputs need $1.5M of additional capital to reach the far side of month 58 — a different conversation from “we have 11 mo”.

• Size the round against the trough plus a buffer, not a number of months. Months are an output; the deficit is the requirement.
• Date the raise from the trough month. Financing takes two to four months when it goes well, so start six to nine months before the trough rather than before zero.
• Watch break-even and the trough together. If break-even lands before the cash runs out, this is a bridging problem. If it never arrives, more cash buys a longer version of the same outcome. That distinction is worked through in operating break-even vs. cumulative payback.

What the model cannot see

All of the following is real and none of it is here.

• Seasonality. Growth and churn are applied evenly to every month. A December renewal cliff or a summer trough produces the same annual total with a far worse intra-year cash position.
• Lumpy hiring. The cost base drifts smoothly. Real ones are step functions: four hires land in March and the figure jumps and stays. Model a planned step by raising the operating cost input and re-reading the trough.
• Working capital and annual prepayment. Revenue arrives in the month it is billed. A customer paying twelve months upfront transforms your cash profile without changing a line of the profit and loss; a large annual renewal does the same in reverse.
• Financing. No debt, no venture capital, no interest on the balance. The line falls until it stops.
• Tax, one-off items and the scenario band. This runs the realistic case only. The full simulator runs conservative and aggressive cases beside it, and the conservative case is the one worth budgeting to.

One last thing: burn is downstream of unit economics. If customers cost more to acquire than they return, cost discipline only changes the date. Check the LTV:CAC and payback calculator before deciding the runway problem is a spending problem.

Educational content, not financial advice. This tool models the assumptions you enter and excludes taxes, financing and one-off items. Check any figure that matters with a qualified accountant before you act on it.