Loan Interest Calculator
Every fixed monthly loan payment is actually two payments in one — a portion covering interest on what you currently owe, and a portion actually reducing the balance. What most people do not realise is how unevenly that split changes over the life of a loan. This calculator breaks down every single month of your loan, showing exactly how much of each payment goes where, and how the balance actually shrinks over time.
Personal Loan Interest Calculator
Calculate total interest, monthly payments and see an amortisation schedule for your personal loan.
Why Early Payments Are Mostly Interest
Interest is calculated each month on whatever balance is still outstanding, which means the very first payment on a loan has the most interest attached to it of any payment across the whole term, simply because the balance is at its highest point right then. As the balance gradually falls, the interest portion of each payment shrinks and the principal portion grows, even though the total monthly payment itself stays exactly the same throughout a standard fixed-rate loan. This is not a flaw or a trick — it is simply how amortised interest genuinely works — but it is a widely misunderstood mechanic, and seeing it laid out month by month makes it considerably more intuitive than a single blended total ever could.
This same mechanic applies to mortgages, car finance and any standard amortising loan, not just personal loans specifically — understanding it once genuinely transfers to reading any repayment schedule more confidently, since the underlying principle behind the shifting split never actually changes between different types of loan.
Watching the Balance Shrink Faster Than It Feels Like It Should
Because more of each payment goes toward principal as the term progresses, the balance does not fall in a straight line — it falls slowly at first and considerably faster toward the end of the term, even though the payment itself never changes. This can make the early months of a loan feel discouraging if you are only watching the balance, since a large early payment can seem to barely dent what is owed. The month-by-month schedule this calculator produces makes that pattern visible directly, rather than leaving it as an abstract concept.
This is worth keeping in mind emotionally as much as mathematically — a loan that feels stubbornly slow to shrink in its early months is not a sign that something is wrong or that repayments are not working; it is simply the normal, expected shape of how amortised debt genuinely behaves, with the visible progress accelerating naturally as the term goes on.
The Same Payment, Two Completely Different Splits
A £10,000 loan at 8.9% APR over five years has a fixed monthly payment of roughly £207.10 throughout. In month one, around £74.17 of that payment is interest, with only about £132.93 actually reducing the balance. By the final month of the term, interest has fallen to around £1.52, with almost the entire £207.10 payment — roughly £205.57 — going toward principal. The payment never changed; only the split inside it did, dramatically, from the first month to the last.
Why Overpaying Early Beats Overpaying Late
Because early payments carry the most interest, an extra payment made early in the loan term reduces the balance while it is still accruing the most interest, producing a larger overall interest saving than the identical extra payment made later, once the balance and its associated interest cost have already fallen considerably. This is the direct, practical consequence of front-loaded interest, and it is exactly why financial advice around overpaying a loan consistently emphasises doing it as early as possible rather than waiting until later in the term, even though the arithmetic of a single overpayment might look similar at first glance regardless of timing.
Reading Your Own Schedule Month by Month
This calculator produces a full month-by-month breakdown for your specific loan, showing the payment, interest, principal and remaining balance at every point across the term, rather than only the headline totals. Expanding the full schedule lets you see exactly which months carry the heaviest interest burden, which is useful both for understanding a loan you already have and for comparing how a shorter term or a lower rate would change that pattern before committing to a specific loan. Our Personal Loan Calculator is useful for a simpler, headline-only view if the full schedule is more detail than you need, and our Cut Your Loan Costs Calculator is worth checking if refinancing an existing loan, rather than just understanding one, is what you are actually trying to work out.
The schedule is collapsed by default and expands on request, keeping the headline totals as the immediate, quick answer while still making the full detail available for anyone who wants to look deeper into any specific point in the term.
Frequently Asked Questions
Does every loan work this way?
Standard fixed-rate repayment loans, where the same amount is paid every month, all amortise this way. Interest-only loans work differently, since the payment covers only interest throughout, with the full balance still owed at the end.
If I overpay, does my monthly payment reduce automatically?
This depends on the lender — some reduce the term while keeping the same monthly payment, clearing the loan sooner, while others recalculate a lower monthly payment over the original term instead. It is worth checking which approach your specific lender applies.
Why does the interest portion never reach exactly zero?
It approaches zero as the balance approaches zero in the final months, since interest is always calculated on whatever balance remains, however small — it simply becomes a negligible amount rather than reaching exactly zero until the balance itself is fully repaid.
Does a shorter term always save interest overall?
Generally yes, since less time means less cumulative interest, even though the monthly payment is higher — the trade-off is a higher monthly commitment in exchange for a lower total cost, which is worth weighing against your own monthly budget capacity.
Can I see how a lump sum overpayment at a specific month would affect the schedule?
This calculator shows the standard schedule without a specific overpayment applied. Running the calculation again with a shorter term or reduced amount reflecting the effect of a planned overpayment is a practical way to approximate the outcome.
Important Information
This calculator provides an estimate based on the figures you enter and does not constitute financial advice. It assumes a standard fixed-rate repayment loan with no missed or additional payments. For advice specific to your circumstances, consult a qualified financial adviser. See our Disclaimer for further information.