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Loan amortisation, explained: interest first, freedom last
The shifting split inside every fixed payment, the three surprises it explains, and how to read your own schedule for the two levers that matter.
Every fixed-payment loan runs on the same hidden schedule, and almost nobody has looked at theirs. Amortisation is the arithmetic that decides how much of each payment buys freedom and how much rents the money — and once you have seen it, three of borrowing's biggest surprises stop being surprises.
The schedule
Take a loan at a fixed rate, repaid in equal instalments. Each payment does two jobs in a shifting split: it pays interest on the current balance — computed on what is still owed, not the original amount — and whatever remains reduces the principal. Because the balance falls, next month's interest slice is slightly smaller and the principal slice slightly larger. Early payments are mostly rent; late payments are mostly purchase. On a typical mortgage the first payment is often eighty percent interest or more; the final payment is nearly all principal. The mortgage guide and the payment calculator run this machine on your numbers; the same arithmetic governs the personal loan, the car loan and the fixed-term consolidation loan alike.
The three surprises it explains
One: why minimum payments on cards feel like running uphill — the card interest guide shows the same split without the forced principal progress, which is what "revolving" really means. Two: why the term is a pricing decision in disguise — stretching a loan from three years to six can halve the payment and nearly double the total interest, because you rent the balance for twice as long. The monthly figure is the number lenders market; the total repayment is the number the schedule contains. Three: why extra payments are disproportionately powerful — an extra amount applied to principal (specify this; some lenders apply surplus to future payments instead) shrinks the balance that every future interest calculation is built on, compounding in reverse across the remaining schedule.
Reading your own schedule
Every lender provides an amortisation table on request or in the app — the full month-by-month split to the final payment. Three things to read on yours. The crossover point, where the principal slice passes the interest slice: it lands later than intuition suggests, and it is a useful marker of how much of the term is "renting." The total interest column: the price of the term you chose. And the effect of a standing extra — many tables let you model one, and watching the end date move years earlier for a modest monthly addition is the most persuasive personal-finance visual there is. The same compounding logic that the compound interest guide celebrates on the savings side is exactly what you are fighting on the borrowing side.
The one-line takeaway: a fixed payment is not a fixed allocation. Every loan is silently back-loaded with freedom, which means two levers do almost all the work — choose the shortest term the budget genuinely survives, and throw any windfall at principal rather than at the next payment. Amortisation rewards both, automatically, on a schedule you can now read.
Sources and further reading
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