Finance & Calculation Tools

Where the maths is exact and where the assumptions are not

It is worth separating two very different kinds of accuracy. The EMI Calculator and Mortgage Calculator are mathematically exact: reducing-balance amortisation is a closed-form formula, and given the same principal, rate, and term, the schedule produced here matches what any lender's system produces. If a lender's figure differs, the discrepancy is almost always in the inputs — fees rolled into the principal, a different day-count convention, or an introductory rate that changes partway through.

The Income Tax Calculator is a different matter. The formulas are applied correctly, but they model standard cases: published rate bands, standard deductions, and the common filing situation. They cannot know about your particular allowances, credits, local levies, or the specific reliefs your circumstances qualify for. That makes them genuinely useful for comparison — which of two salary offers leaves more in hand, roughly what a raise is worth after tax — and unsuitable as the basis for an actual filing.

The comparisons worth running before you commit

For a loan, the figure that changes decisions is rarely the monthly payment — it is total interest over the full term. A longer term lowers the monthly number and raises the total cost, often dramatically, and seeing both together is what makes that trade-off concrete rather than abstract. The same applies to overpayments: modelling even a modest regular extra payment usually shows a surprisingly large reduction in both total interest and term length, because early overpayments attack the principal when the balance is at its highest.

For salary, gross figures are close to meaningless across borders. Two offers with the same headline number in different countries can differ substantially once income tax, social contributions, and mandatory insurance are applied. Running both through the Salary Calculator puts them on a comparable basis, which is the only way the comparison means anything.

For GST and invoicing, the recurring error is confusing inclusive and exclusive pricing. Adding a tax rate to a price that already includes it overstates the total, and the reverse understates what you owe. The GST Calculator handles the reverse calculation directly if you quote tax-inclusive prices to customers but your accounting expects exclusive figures — and once the number is right, the Invoice Generator is where it actually goes out the door.