Cumulative Budget Calculator

Most budget calculators tell you what one average month looks like. That is the month you never actually live. This one carries every month forward — surpluses and shortfalls both — and shows the running balance you will really have, including the annual bills that land all at once.

Recurring monthly costs

One-off & annual bills (the ones that wreck a month)

Project for
Monthly surplus
1,670 CHF
before one-off bills
Balance after 12 months
19,640 CHF
cumulative, carried forward
Total spent
24,360 CHF
over the whole period
You stay in the black for all 12 months. The running balance never drops below zero, with 3,670 CHF at the tightest point.
Running balance
Oct 26Dec 26Feb 27Apr 27Jun 27Aug 27
MonthIncomeSpentNetRunning balance
Oct 263,500 CHF1,830 CHF1,670 CHF3,670 CHF
Nov 263,500 CHF1,830 CHF1,670 CHF5,340 CHF
Dec 263,500 CHF1,830 CHF1,670 CHF7,010 CHF
Jan 27+ one-off3,500 CHF2,730 CHF770 CHF7,780 CHF
Feb 273,500 CHF1,830 CHF1,670 CHF9,450 CHF
Mar 273,500 CHF1,830 CHF1,670 CHF11,120 CHF
Apr 273,500 CHF1,830 CHF1,670 CHF12,790 CHF
May 27+ one-off3,500 CHF3,330 CHF170 CHF12,960 CHF
Jun 273,500 CHF1,830 CHF1,670 CHF14,630 CHF
Jul 273,500 CHF1,830 CHF1,670 CHF16,300 CHF
Aug 273,500 CHF1,830 CHF1,670 CHF17,970 CHF
Sept 273,500 CHF1,830 CHF1,670 CHF19,640 CHF

Everything is calculated in your browser — no numbers are sent anywhere, and nothing is saved.

This calculator works on the figures you type once. The Cumulative Budget app keeps the same projection alive from your real income and expenses — including shared accounts and recurring entries — so the curve updates itself and warns you before the balance dips.

Try Cumulative Budget free →

How the calculation works

A traditional monthly budget treats each month as a sealed box: income in, expenses out, and whatever happened is forgotten on the 1st. A cumulative budget refuses to reset. Every month starts from where the last one ended, so a 200 overspend in March is still with you in September unless you earn it back.

Running balance (this month) = running balance (last month) + income − recurring costs − one-off bills

The calculator applies that formula once per month across your chosen horizon. Recurring costs repeat every month; one-off bills are charged only to the month you place them on. The result is a line rather than a number — and the shape of that line is what tells you whether the plan survives contact with reality.

How to read your result

  • A steadily rising line means your surplus is real and compounding. The steeper it is, the faster you can bring a savings goal forward.
  • A sawtooth — climbing, then dropping sharply — is the signature of lumpy annual bills. The budget is fine; the timing is not. Spreading or pre-funding those bills flattens it.
  • A line that drifts down means the monthly maths is wrong, not the timing. No amount of rescheduling fixes it: income has to rise or recurring costs have to fall.
  • The crossing point — where the line hits zero — is your deadline. Everything you do before it is planning; everything after it is damage control.

What to try next

Change one input at a time and watch the crossing point move. Cutting a subscription shifts it by days; moving a holiday to a month with more room can shift it by months. That sensitivity is the useful part — it shows which decision actually buys you breathing space, instead of the generic advice to spend less.

If you want the same picture kept up to date automatically, that is exactly what Cumulative Budget does with your real entries — including shared household accounts, recurring items and goals.

Frequently asked questions

How is a cumulative budget calculated?

Each month you add your income and subtract everything you spent that month, then carry the result into the next month instead of resetting it. The formula is: running balance (this month) = running balance (last month) + income − expenses. Because nothing resets, a tight month never disappears — it follows you forward until you make it up.

What does the running balance line tell me?

Its slope is your real burn rate. A rising line means you are adding money faster than you spend it; a flat line means you are breaking even; a falling line means every month costs more than it brings in. The point where the line crosses zero is the month you run out — and seeing it months ahead is the whole point of projecting.

Why do one-off bills matter so much?

Monthly budgets hide them. An annual insurance premium or a holiday looks affordable when you average it across twelve months, but it does not arrive in twelve pieces — it lands on one day. A cumulative projection puts it on the month it actually hits, which is usually where an otherwise healthy budget breaks.

Is my data saved or sent anywhere?

No. This calculator runs entirely in your browser. Nothing is uploaded, stored or logged, and closing the tab discards the figures.

How much should I keep as a buffer?

A common starting point is one month of recurring costs, then three to six months as a full emergency fund. Use the calculator to find your lowest point over the next year: if the tightest month is close to zero, that gap is the buffer you are missing.

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