Monthly expenses and savings calculator

A fixed cost is the same every month whether you do anything or not: rent, the home or car loan instalment, insurance, a software subscription, a salary. A variable cost moves with how you live or trade: petrol, groceries, electricity, supplies, delivery charges, eating out. Both belong in this list, because both leave the account. The reason the split is worth knowing is that it tells you where a cut is even possible. Fixed costs can usually only be changed by a decision that takes months — moving house, refinancing, letting a subscription lapse at renewal — while variable costs respond this week. A budget that is 90% fixed is not a budget you can trim in an emergency, however small the total looks, and that is a fact about the shape of the list rather than about its size.

Switch that row to Yearly, enter the annual amount, and the calculator divides it by twelve for the monthly total. Insurance premiums, road tax, quit rent and assessment, professional membership fees, an audit fee, school registration, a domain or hosting renewal — these are the bills that ambush a budget that otherwise balances, because they are absent for eleven months and then arrive in one lump. Dividing them across twelve does two things: it gives you a monthly figure that is honest about what you owe, and it tells you exactly how much needs to be sitting aside by the time the bill lands. The division is done and rounded to the cent on the row itself, so the number you see in the row is the number added to the total — the column always adds up to the figure printed under it.

It means treating the amount you save as a bill you owe yourself, taken out at the start of the month, rather than as whatever survives to the end of it. The order matters more than the amount. Money that is left in a spending account at the end of the month has, in practice, already been spent — that is what "left over" turns out to mean for most people, most months. That is why the saving field here is separate from what is left after expenses instead of being calculated from it. There is a button to copy the leftover figure across when you want it, but you are free to set the saving first and then adjust the expense rows until the two fit. If the saving you set is larger than what is left, the page says so rather than quietly showing a negative balance somewhere.

Because any rate this page used would be a number we invented. Savings account rates differ by bank, by product, by balance tier and by month; fixed deposit rates depend on tenure and on when you lock in; investment returns are not a rate at all, they are a range with a real chance of being negative. Printing "your savings will grow to X" from an assumed 3% would look authoritative and would be wrong for nearly every visitor, and it would be wrong in the flattering direction. So the projection here is deliberately plain: it is the amount you save multiplied by the number of months, and nothing else. Whatever interest you do earn is a bonus on top of a figure you can verify with a pocket calculator. This is the same reason no public holidays are built into our days calculator and no legal fees are guessed at on the mortgage page — a plausible invented number is harder to catch than a missing one.

The page says the target is never reached at that rate, in plain words. It does not print "Infinity months" and it does not silently show a blank. Dividing a target by a saving of zero is exactly where a calculator either crashes or produces nonsense, and the honest answer is not a number at all — at zero a month, no amount of time gets you there. The same applies when the saving is so small relative to the target that it would take more than a hundred years: the page says the target is beyond a lifetime at that rate rather than printing a figure in the thousands of years, which reads like a bug. If you see either message, the useful move is to change the inputs — a bigger monthly saving, or a smaller target — and watch the months fall.

This page will not tell you, and that is deliberate. The right share depends on things a calculator cannot see: how many people the income supports, whether the home is rented or being bought, whether there is a car loan or a bus pass, what the medical situation is, and how much debt is already being serviced. Rules of thumb exist and people quote them confidently, but they were written for particular countries, particular decades and particular household shapes, and applying one to a household it was not written for produces a number that feels authoritative and means nothing. What the percentage here is genuinely good for is comparison against itself. Work it out this month, keep the file, work it out again in six months, and the direction of travel tells you something real about your own budget — which is a measurement, not advice.

No. Every figure is worked out in your browser, and nothing you enter is sent anywhere — there is no server here to send it to. Your list does stay in your browser storage on this device, on purpose, because a household budget is built over several days rather than in one sitting and losing it when a tab closes would be the wrong behaviour. That means it is saved locally and it survives a refresh; it also means clearing your browser data, or using a different device or a private window, gives you a fresh empty list. If you are on a shared computer and would rather not leave it behind, clear the browser data for this site when you are done, or export the CSV and use the reset control.

Yes. It is a plain comma-separated file with one row per expense — the label, the amount as billed, whether that amount is monthly or yearly, and the monthly share — followed by a summary block carrying income, total expenses, what is left, the percentage, the monthly saving, the six-month, one-year and five-year projections, the target and the time to reach it. The numbers are written raw, as 1234.56 rather than 1,234.56, because a number carrying thousands separators lands in a spreadsheet as text that will not sum, and it fails silently: the file opens, the column looks fine, and SUM returns zero. The currency symbol goes in the column heading instead, where it tells you what the figures are without breaking them. Fields containing a comma or a quotation mark are quoted and internal quotes are doubled, so a row named "Utilities (water, electricity)" does not shift every column after it.