The monthly payment is the number people ask for. The total interest is the number that decides whether the purchase made sense.
This calculator runs entirely in your browser. No figure you enter is transmitted, stored or logged — the page makes no network request while you use it. The model is a simplified illustration of standard arithmetic and is not investment, tax, legal or lending advice, and not an offer. Real outcomes depend on contract terms, fees, taxes and your own circumstances.
A fixed-rate loan is repaid by a constant monthly amount in which the interest share falls and the principal share rises over the term.
Payment = L × r / (1 − (1 + r)−n), where r is the monthly rate and n the number of months. Nothing more exotic is involved.
Extending a term lowers the monthly payment and raises total interest, often sharply. Move the term slider and watch the interest share.
Amortisation requirements, imputed rental value, property taxes, insurance and arrangement fees are not modelled. Local lending rules vary considerably.
The judgement that matters is what you do with the answer.
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