The core calculation
The calculator uses one formula with two steps. Both steps are simple arithmetic, no models, no algorithms, no black boxes.
Step 1: Monthly Spending − Monthly Income = Monthly Burn Rate
Burn rate is how much your savings shrink each month. If income covers spending, burn rate is zero or negative, meaning savings are stable or growing.
Step 2: Savings ÷ Monthly Burn Rate = Months of Runway
Runway is how many months your savings would last at the current rate.
Example: $15,000 savings · $3,500 spending · $2,000 income. Burn rate = $1,500/month. Runway = 15,000 ÷ 1,500 = 10 months.
If income equals or exceeds spending, burn rate is zero or negative. The result is flagged as indefinite, meaning savings are not decreasing at current levels.
The three inputs
Current savings: the total in accessible accounts you would draw on if your income stopped. Typically a savings account or cash buffer. Do not include pension funds you cannot access yet, or investment accounts you would only liquidate in a genuine emergency.
Monthly spending: everything you spend in a month: rent, groceries, transport, subscriptions, dining out, occasional purchases. If you are unsure, check your last two bank statements and use the average. Most people underestimate this by 15-25%.
Monthly income (optional): your regular take-home income after tax. If your income is irregular, use a conservative monthly average. Leave it blank or enter 0 if you have no income right now.
The six runway tiers
Your result places you in one of six tiers. Each comes with a different label, spending nickname, roast, and set of tips calibrated to where you actually are, not a generic response.
0-1 months. Immediate, concrete action is the only meaningful response. Focus on cutting expenses and finding income this week, not sometime soon.
1-3 months. Urgent but not yet critical. Small deliberate changes started now can extend the runway before it becomes an emergency.
3-6 months. A functional buffer, but not a comfortable one. Use this breathing room to push toward 6 months, not to relax.
6-12 months. Solid position with real options: the ability to handle an unexpected bill, leave a bad situation, or make a deliberate financial move.
12+ months. Strong financial resilience. The question shifts from survival to optimisation. Are your savings working as hard as they could be?
Stable. Income covers spending. Savings are protected or growing. The focus moves to putting any surplus to work productively.
Roast mode, Coach mode, or both
You choose the tone before calculating:
- 🔥 Roast Me: a short piece of comedic writing based on your tier. Comments on the situation, never your worth or intelligence. Makes the result memorable.
- 💡 Coach Me: skips the roast and goes straight to three practical tips tailored to your tier. No jokes, just useful starting points.
- 🔥💡 Roast + Coach: shows both. The default. The roast makes it stick; the tips make it useful.
Three tips are shown at random from a larger pool for each tier, so recalculating may surface different suggestions.
The savings projection graph
After calculating, a graph shows how your savings are projected to change over time at the current burn rate:
- Positive burn rate → line slopes down to $0, showing when savings are projected to run out
- Zero burn rate → flat line, savings hold steady
- Income exceeds spending → line slopes upward, showing savings growth
Milestone cards below the graph show your projected balance at 3, 6, and 12 months. This is a linear projection assuming constant spending and income, an estimate, not a forecast.
The What-If simulator
Below the result card, the What-If section shows how small adjustments would change your runway without re-entering your numbers. Six scenarios: cutting spending by $100, $250, or $500 per month, and adding $100, $250, or $500 in monthly income.
Each shows the impact in concrete terms, for example, “+3.2 months extra” or “Income covers spending.” This turns abstract advice (“spend less”) into a specific, testable number (“cutting $250/month adds 3 months to my runway”).
Your data stays in your browser
The calculation runs entirely in your browser using JavaScript. Your savings, spending, and income figures are never sent to any server, stored in a database, or logged anywhere. No account, no signup, your numbers never leave your device.
See the Privacy Policy for the full details, including what third-party services (hosting, fonts, advertising) may collect.
Limitations
The calculation is intentionally simple. It does not factor in inflation, investment returns, tax, variable income or spending, debt repayments, or future life changes. The result is best read as: if nothing changes from today, here is roughly how long your savings would last.
That is useful enough to act on, which is the point. For a fuller picture, see the full disclaimer or speak to a qualified financial advisor.
This page is for general education and informational purposes only. It does not constitute personalised financial advice. Every situation is different. For decisions involving significant money, please speak to a qualified financial professional. Read our Editorial Standards and full disclaimer.