Cash Balance vs Runway: What Founders Should Track Weekly
Your bank balance can lie to you. Runway tells the truth. Here's the difference, how to calculate runway correctly (with a worked example), the mistakes to avoid, and the 5-minute weekly habit.
Abrar Masum
ZeroFin
Two founders each have money in the bank. One has six weeks of runway; the other has eight months. The bank balance won't tell you which is which — and that's exactly why it's the wrong number to obsess over.
The short answer
Your cash balance is what's in the account today. Your runway is how long you survive given what's actually coming in and going out. Runway = current cash ÷ average monthly net burn. Track runway weekly; track balance only as an input to it.
Key takeaways
- Cash balance is a snapshot; runway is the trend that actually matters.
- Use a 3-month average for net burn — never a single month.
- Use net burn (after revenue), not gross burn.
- Runway is really a deadline: enough time to hit your next milestone?
Why the bank balance lies
A healthy-looking balance can hide a fast leak, and a scary-looking one can be totally fine. Balance is a single frozen moment; your business is a flow.
Company A
- $200,000 in the bank
- $50,000/mo net burn
- → 4 months of runway
- Looks rich. Isn't.
Company B
- $40,000 in the bank
- $5,000/mo net burn
- → 8 months of runway
- Looks tight. Safer.
Same question — “how much cash do you have?” — wildly different answers about survival. Company B, with one-fifth the balance, has twice the runway.
How to calculate runway (correctly)
- 1
Find your net burn
Net burn = average monthly (cash out − cash in) over the last 3 months. Averaging three months smooths out one unusually good or bad month.
- 2
Divide cash by net burn
Runway (months) = current cash ÷ net burn. That's it.
Worked example
You have $120,000 in cash. Over the last 3 months your average net burn was $20,000/mo. Runway = 120,000 ÷ 20,000 = 6 months.
The two mistakes almost everyone makes
Avoid these
1. Using gross burn (ignoring revenue) — too pessimistic and hides whether revenue is helping. 2. Using a single month — too noisy; one big invoice or annual bill distorts everything. Always use net burn over a 3-month average.
The real question runway answers
Runway isn't a vanity metric — it's a deadline. The useful version of the question is: “Is my runway long enough to hit the milestone that unlocks my next raise (or profitability)?” That reframes runway from anxiety into planning.
The 5-minute weekly habit
Check these every week
- Cash balance across all accounts
- Net burn trend — is it growing?
- Runway in months
- What changed since last week — and why
If pulling those numbers takes more than five minutes, the problem isn't the math — it's that your books aren't current enough to trust. Fix the foundation and these become a glance.
“Profit is an opinion. Cash is a fact. Runway is the deadline that fact gives you.”
Frequently asked questions
What is the difference between cash balance and runway?
Cash balance is the money in your accounts right now. Runway is how many months you can operate before running out, calculated as current cash divided by average monthly net burn.
How do I calculate runway?
Runway = current cash ÷ average monthly net burn, where net burn is the average of (cash out − cash in) over the last three months.
What is a healthy runway for a startup?
Many investors suggest keeping 12–18 months of runway after a raise, and not letting it drop below ~6 months without a clear plan to extend it or raise again.
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