Financial Runway: How to Calculate How Long Your Money Would Actually Last

A startup that has $400,000 in the bank and burns $50,000 a month does not have “$400,000.” It has eight months of runway — and every founder knows that runway, not balance, is the number that runs the company. Personal finance has the same number, and almost nobody calculates it. People know their emergency fund balance. They know their net worth. They do not know how many months of their actual life that balance buys, which is the only number that matters the day a job ends, a contract dries up, or a sabbatical starts.

This guide is the full calculation. Three inputs, four lengths, and the haircuts most people skip — taxes, locked accounts, currency exposure, the lifestyle compression you can and cannot actually do. The output is a single number in months. You should know it the way you know your weight.

Runway Is Not Your Emergency Fund

These two get confused constantly and they answer different questions.

An emergency fund is a target — a sized reserve, usually 3–6 months of essential expenses, held in a savings account, designed to absorb a single bad event. The question it answers is “do I have enough cushion to not panic.” It is a static number you build toward.

Financial runway is a diagnostic — a current reading of how long your total liquid wealth sustains your current life, today, at today’s prices, before any heroic cuts. The question it answers is “if income stopped right now, when would I run out.” It is a dynamic number that changes every month with both sides of the equation.

The emergency fund is one input into the runway. So is your brokerage account, your crypto, your cash. So is the burn rate that includes the gym membership you would not actually cancel for six weeks of unemployment. Runway is the honest version of the question.

The Calculation

Three inputs. Each one has a haircut most people forget.

Input 1: Liquid Assets (with haircuts)

Liquid means accessible within roughly two weeks without a major loss. Add up:

• Checking and savings accounts — full value.
• Brokerage account (taxable) — face value minus an estimated 15–25% capital gains haircut on the gains portion, and minus a 5–10% market drawdown reserve. If your $80,000 brokerage account is half gains, you might book it as ~$70,000 of true accessible value, not $80,000.
• Crypto held in self-custody or on a major exchange — face value minus a 20–30% volatility reserve if the position is large enough to matter. Crypto is liquid in hours; it is also liquid at 60% of last week’s price.
• Money market funds, short-term Treasuries — full value, minus any early-withdrawal penalty.
• Cash value of permanent life insurance, if any — only if you would actually borrow against it; usually exclude.

Do not include:

• Retirement accounts (401(k), IRA, pension, ISA, KiwiSaver, etc.) — taxes and penalties make them effectively illiquid for runway purposes. Track them for net worth, exclude them from runway.
• Home equity — a HELOC is not runway, it is a credit line that disappears when you lose your job.
• Equity in a private business — illiquid by definition.
• Cars, jewelry, “collectibles” — non-liquid; selling at a fire-sale discount is not a plan.

The result is your accessible liquid base. This is the numerator.

Input 2: True Monthly Burn (with the cuts you would actually make)

This is where almost everyone overestimates their runway. They divide their balance by their average historical spend, which includes vacations, restaurant meals, gifts, gear, and a Black Friday TV. Real runway uses two burn numbers:

• Current burn — the trailing 3-month average of total outflows, including the discretionary stuff. This is what your life costs if nothing changes.
• Compressed burn — what your life would cost after two specific cuts you would actually make in the first 30 days of no income: pause vacations and large purchases, drop the top three discretionary categories by half. This is not “rice and beans” — that fantasy never survives contact with month two.

A typical pattern: current burn $4,200, compressed burn $3,100 — about 25% lower, achievable, sustainable. The 40% and 50% cuts you read about online assume a level of discipline that is not borne out in any real freelance drought or job loss.

If your income is irregular, use a 6-month trailing median for current burn rather than an average — a single big quarter throws averages off badly. See variable-income budgeting for the full method.

Input 3: Fixed Obligations You Cannot Cut

Some of your burn cannot be compressed in the first three months at any cost. List them separately:

• Rent or mortgage payment
• Insurance premiums (health, car, life)
• Minimum debt service on loans and credit cards
• Childcare, school fees, alimony
• Utilities at the legally-required minimum

Call this your fixed floor. If your fixed floor is $2,400, no amount of frugality gets your monthly burn below that without a major life change (move, sell the car, switch insurance). The fixed floor sets the ceiling on how much runway extension is possible without disruption.

The Four Runways

Once you have liquid base, current burn, compressed burn, and fixed floor, compute four numbers:

A worked example. Liquid base $42,000 (after haircuts). Current burn $4,200. Compressed burn $3,100. Fixed floor $2,400.

• Comfortable: $42,000 ÷ $4,200 = 10.0 months
• Practical: $42,000 ÷ $3,100 = 13.5 months
• Survival: $42,000 ÷ $2,400 = 17.5 months
• Crisis: ($42,000 − $2,400) ÷ $3,100 = 12.8 months

The headline number — the one to memorize and re-check quarterly — is practical runway. Comfortable is optimistic, survival is fantasy, crisis is a tighter version of practical. Practical is the number that holds up.

What Erodes Runway Faster Than You Think

Five forces that shorten the number you just computed:

Inflation on the fixed floor. Rent goes up, insurance goes up, food goes up. A 5% inflation year erodes survival runway by roughly five months out of every hundred. Rebuild the number annually, not “when something changes.”

Tax timing. If you have stock vesting, a freelance balance due, or self-employment quarterly estimates coming, those are real liabilities sitting against your liquid base. Subtract them from the numerator before you compute. A $42,000 base with $8,000 of incoming tax is really $34,000 — and your practical runway just dropped from 13.5 to 11.0 months.

Account-access delays. Brokerage settlement is two business days. Bank transfers from neobanks can hold for 5–10 days on large amounts. Crypto on-chain transfers are fast; off-ramping to fiat through a regulated exchange is often a week. You cannot fund week one of unemployment from week one’s brokerage sale. Keep at least one month of fixed floor in a checking or instant-savings account that needs no settlement.

Currency exposure. If you earn in one currency and spend in another (common for expats, freelancers with foreign clients, anyone in a multi-currency life), runway in your spending currency moves with FX. A 10% drop in the currency your savings sit in cuts runway by 10% overnight, before you have spent anything. Hedge or hold a working balance in spending currency.

Health and life events. A medical bill, a partner losing income at the same time, a car that needs replacement, an immigration deadline that forces a country move. None of these are in your monthly burn until they happen, and then they consume two to four months of runway in a single transaction. The way to absorb this is not a bigger emergency fund inside the runway — it is keeping practical runway above 9 months so a single $5,000 shock does not reset the clock.

The Targets

There is no universal right number, but there are honest defaults:

• Under 3 months practical runway: acute exposure. One bad event ends in debt. Treat this as urgent — build practical runway as the only financial priority until it crosses 3.
• 3 to 6 months: the standard emergency-fund zone. Sufficient for an average job loss in a healthy market, insufficient for anything else.
• 6 to 12 months: comfortable. Lets you decline a bad offer, take a 3-month sabbatical with margin, ride out a contract drought without panic.
• 12 to 24 months: strategic. Buys you the option to take a job at lower pay because you want to, or to start something. This is the range that converts runway from defense into offense.
• Over 24 months: approaching mini-retirement territory. Rare to need more than this unless you are deliberately moving toward financial independence.

The practical runway you target depends on three things: how replaceable your income is (a specialized W-2 role with high market demand needs less than a niche freelance specialty), how compressible your burn is (a low fixed floor lets a small runway stretch further), and how many dependents share your runway (every additional dependent roughly halves how exposed you are willing to be).

Common Mistakes

Counting retirement accounts. They double your number and lie about it. Keep them out of runway.

Using face value of stocks at peak. The 2022 drawdown wiped 25% off many portfolios in nine months. Book brokerage at a haircut so a normal correction does not surprise your runway.

Forgetting the tax bill that’s coming. Freelancers in particular: a $12,000 Q1 estimated payment due in April is not optional. It comes out of the numerator.

Mistaking credit lines for runway. A HELOC, a credit card limit, a margin loan facility — these all get pulled, frozen, or repriced exactly when you need them. Credit is not runway.

Confusing one-month-cut bravado for compressed burn. “I’d just stop everything” works for 30 days. By day 45 you are buying the things you said you would not buy, because compression has a half-life. Use a realistic compressed burn, not a fantasy one.

Not recomputing. Runway changes every month. A two-year-old runway number is a story, not a calculation. Re-do it quarterly, ideally at the same cadence as your quarterly review.

How Thrust Handles This

Thrust is built so the runway calculation is something you read off the dashboard, not something you reconstruct from a spreadsheet every quarter.

• Unified liquid net worth. Checking, savings, brokerage, crypto across 18 blockchains, precious metals — everything sits in one ledger with live exchange rates across 20+ currencies. The numerator updates itself.
• Trailing burn from real transactions. Your 3-month and 6-month burn rates compute from your actual categorized spending — current burn is a number, not a guess. Smart Tags let you separate one-off events (a wedding, a move) from steady-state burn so the trailing average is not polluted.
• Safe-to-Spend with horizon. On-device AI surfaces what you can spend today without breaking your trajectory. It is the daily version of the runway question — the same calculation, recomputed every morning against your bills, goals, and balance.
• What-If scenarios. Model “what if I lose income next month” or “what if rent goes up 8% in November” and see the runway impact before it happens. The forecast runs offline on your device, with GPU acceleration — no data leaves the phone.
• Subscription detection. Recurring charges are surfaced so the compressed-burn cuts are obvious targets, not detective work.
• Multi-currency runway. If you earn in EUR and spend in PLN, the app holds both — you see runway in your spending currency at today’s rate, with FX drift visible in the trend.
• Ghost Mode by default. All of this runs on-device. There is no server-side account, no cloud sync of your balances, no analytics. The most sensitive number in your finances stays on the phone.

Thrust is free on the App Store. The runway dashboard works on day one with manual entries or a CSV import; receipt scanning and voice input fill in the rest as you go.

Close

The reason most people do not know their runway is that they do not want to. The number is honest in a way an emergency-fund target is not — it includes the spending you keep meaning to cut and the taxes you keep meaning to set aside. The day you compute it is the day you have to look at both. Do it anyway. Knowing you have 11 months of practical runway, not 6, is the difference between negotiating from strength and taking the first offer that lands. The calculation takes 30 minutes the first time and 5 minutes every quarter after that. Start now.