Work & Money

Two kinds of question, and they are not the same job

The first three tools settle something that has already happened or is happening now: what a week of shifts came to, what an hourly rate is as an annual salary, what this month’s payment is. There is a right answer, you can check it against a payslip, and the tool is doing arithmetic you could do by hand if you had the patience.

Everything else is a projection. Compound interest, retirement savings, rent against buying, whether a degree of debt clears faster by snowball or avalanche — these depend on assumptions about years you have not lived yet. The arithmetic is still exact, but the answer is a consequence of your inputs rather than a fact about the world, and every one of these tools shows the inputs it used for exactly that reason.

What the money tools deliberately do not know

None of them knows your tax position. There is no tax code, no filing status, no allowances and no local rates anywhere in this category, and that is a design decision rather than an omission: tax rules differ by country, by state or province, by year and by circumstance, and a calculator that quietly applies one set of them to everybody is wrong for most of its users while looking authoritative to all of them.

So gross is gross. The time card calculator gives you gross pay; the hourly-to-salary converter converts gross to gross. Where a figure genuinely depends on a rule, the rule is an input you choose from named options rather than a constant baked in — the affordability calculator is the clearest instance, offering the traditional US 28/36 rule, the FHA 31/43 benchmark, Canada’s GDS 39 / TDS 44 limits and a UK income multiple, because those are four different lenders’ answers to one question and there is no neutral one.

Compounding, and the detail that makes a mortgage wrong

A loan’s cost is decided by two things: the rate, and how often the rate is applied. Get the second wrong and every figure downstream is subtly off — not dramatically, not obviously, just consistently, in a way that shows up as a few hundred pounds or dollars by the end of a term.

US mortgages compound monthly. Canadian ones are conventionally written on semi-annual compounding, which follows from a disclosure rule in the Interest Act rather than from a cap on how often interest may compound. That is not a rounding difference; it is a different formula, and running the US one for a Canadian borrower produces a payment that does not match the lender’s. The mortgage calculator here asks which you want rather than assuming, and converts the semi-annually compounded rate to its monthly equivalent when you pick Canada.

The same principle drives the rest of the group. The compound interest calculator lets you set the compounding frequency instead of assuming annual. The credit card payoff tool answers the question a statement does not: whether your payment covers the interest at all, because below a certain payment the balance never falls no matter how long you keep paying.

Where to start, depending on what you are deciding

Time Card Calculator

A week of shifts with unpaid breaks, split into regular and overtime.

Mortgage Calculator

A payment and a full amortisation schedule, on US or Canadian compounding.

Home Loan Affordability Calculator

How much a lender is likely to think your income supports, under a rule you pick.

Debt Payoff Planner

Several debts at once, and whether snowball or avalanche costs less.

Loan Payoff Calculator

One loan, and what paying extra each month does to the end date.

Rent vs Buy Calculator

The comparison that counts what a renter would have earned on the deposit.