How much cash should you actually keep? The runway math

Last updated June 2026

“Keep three to six months of expenses” is the advice everyone gives and almost nobody sizes correctly. Too little and a job loss becomes a forced sale or a credit-card spiral. Too much and you're quietly losing thousands a year to inflation and missed returns. The right number isn't a slogan — it's a calculation from your spending and your income stability.

Start with runway, not a round number

Your cash runway is how long your liquid cash would cover you with no income:

runway (months) = liquid cash ÷ essential monthly spend

Note essential spend — rent or mortgage, food, utilities, insurance, minimum debt payments — not your normal month. In a real emergency you cut the dinners-out and the subscriptions, so sizing the buffer against bare-bones spending is both honest and cheaper.

How many months you actually need

The right target moves with how reliable your income is and how fast you could replace it:

3 months — stable salary, dual income, in-demand skills, no dependents.
6 months — single income, a mortgage, or a role that takes a while to re-hire for.
9–12 months — variable or commission income, self-employed, equity-heavy pay, or a niche field.

If a big chunk of your compensation is bonus or RSUs, treat only your base as reliable when you size the buffer — the variable part is exactly what disappears in a downturn.

The cost of too much

Cash feels safe, and a buffer should be. But money beyond your runway is the most expensive “safety” you own. Sitting on an extra $40,000 earning near-zero while inflation runs a few percent can quietly cost $1,000–$2,000 a year in lost purchasing power — before counting the returns it could have earned. A high-yield savings account or money-market fund recovers much of that with no real loss of access.

A simple framework

Buffer: your runway target, in a high-yield account you can reach same-day.
Sinking funds: known near-term costs — taxes, insurance, a trip — kept separate so they don't masquerade as emergency cash.
Everything above that: has a job to do — invest it, pay down high-interest debt, or fund a goal. See the tax-aware way to move money when you do.

How Orbeva watches it for you

Orbeva reads your real, connected accounts to compute your actual essential spend and your live cash runway — then flags when your buffer drifts thin or when idle cash has piled up past what you need, with the move worth reviewing. It watches the risks others ignore, from concentration to margin distance. It's read-only — you make every transfer yourself.

See your cash runway — start free →

General information and decision support, not financial advice. Your right buffer depends on your full situation; consider a professional for big decisions.