Loan Payment Calculator

The number you have to live with

Every loan conversation ends up at the same question. Not how much you are borrowing, not what the rate is, but what leaves your account each month and whether you can carry it.

This calculator answers that one. Amount, rate, term, how often you pay, and it gives you back the instalment, the number of instalments, the periodic rate you are actually being charged, and the total you will have handed over by the end.

The total is the row worth looking at twice. Instalments are designed to feel manageable, which is their whole purpose, and the sum of them frequently is not. Seeing both figures next to each other is the cheapest financial education available.

Five fields

1. Loan Amount. What you are borrowing, after any down payment has come off.
2. Annual Interest Rate. The rate quoted per year, as a percentage. There is a section below on making sure this is the right kind of rate, and it is the most important thing on this page.
3. Loan Term. Two boxes, years and months, so a thirty month loan can go in as 2 and 6 rather than 2.5.
4. Payment Frequency. Monthly, quarterly or annually.

Press Calculate and you get four results: the number of instalments, the periodic interest rate, the instalment itself, and the total of all payments.

That second result is more useful than it looks. It tells you what you are charged per payment period rather than per year, which is the figure your instalment is actually built from. On a quarterly loan at 10 percent a year, the number that does the work is 2.5 percent per quarter.

How the frequency reshapes the sum

The instalment comes from the standard amortising formula, the same one every bank uses:

Payment = L × i ÷ (1 - (1 + i)^-n)

What the frequency dropdown does is decide what i and n mean.

• n is the number of payments: your term in years multiplied by the number of payments in a year. Five years monthly is 60, five years quarterly is 20, five years annually is 5.
• i is the rate per payment period: your annual rate divided by the number of payments in a year. Ten percent a year is 0.8333 percent a month, 2.5 percent a quarter, or 10 percent a year.

Then the total is simply the instalment multiplied by the number of instalments.

Dividing the annual rate straight by the number of periods is the ordinary convention for quoted lending rates, in South Asia and across most of the world. It treats your quoted rate as a nominal annual rate cut into equal slices. If a lender quotes an effective annual rate instead, that is a different number and the instalment will differ slightly, so it is worth asking which one you have been given.

Ten thousand at ten percent over five years

Small, round and easy to follow. Loan 10,000, rate 10 percent, term 5 years, paid monthly.

Number of payments: 5 × 12 = 60. Periodic rate: 10 ÷ 12 = 0.8333 percent a month.

Through the formula, the instalment is 212.47.

Sixty payments of 212.47 is 12,748.23. So borrowing 10,000 costs you 2,748.23 in interest, which is a bit over a quarter of what you borrowed, for a loan most people would describe as short.

That ratio is worth carrying around. At 10 percent over five years, roughly a quarter on top. At the same rate over ten years it is closer to half, because the money is out for twice as long. Term does more damage than people expect, and it does it quietly, because a longer term is always sold as the smaller instalment.

What the frequency dropdown costs you

The frequency looks like an administrative detail. It changes what the loan costs.

Same 10,000, same 10 percent, same five years, only the frequency moved:

Paying once a year rather than once a month costs an extra 441.64 on a 10,000 loan. Nothing about the deal changed except how often money moves.

The reason is that interest is charged on what you currently owe. Pay monthly and the balance steps down twelve times a year. Pay annually and it sits untouched for a full twelve months, earning the lender interest on money you would otherwise have repaid.

So where a lender offers a choice, more frequent is cheaper. Where your income arrives in lumps, from a harvest or a contract or a seasonal business, quarterly or annual may still be the right structure, and now you know what the convenience costs.

Flat rate or reducing balance, and why it matters enormously

This is the single most important thing on the page, and it is the one most likely to make your answer wrong.

There are two completely different ways a lender can quote interest on an instalment loan.

Reducing balance charges interest on what you currently owe. As the balance falls, the interest falls with it. That is what this calculator computes, and it is how mortgages and most bank loans work.

Flat rate charges interest on the original amount for the whole term, regardless of how much you have repaid. Borrow 10,000 at 10 percent flat for five years and the interest is 10,000 × 10 percent × 5 = 5,000, full stop, even though your average balance across those five years is nowhere near 10,000.

Flat rates are common on personal loans, vehicle finance and consumer credit across South Asia and much of Asia, and they sound far cheaper than they are.

Here is the comparison on that same loan:

Same headline percentage. Nearly double the interest.

Put the other way round, a 10 percent flat rate is equivalent to roughly 17.3 percent on a reducing balance. That multiplier stays remarkably steady across terms, sitting somewhere between 1.7 and 1.8 times for the loan lengths people usually take. So a quick mental rule: a flat rate is worth about 1.8 times itself in real terms. Twelve percent flat is around 21 percent reducing. Fifteen percent flat is around 27 percent.

What this means for the box on this page: if your lender quoted a flat rate, do not type it in here. You will get an instalment of 212.47 when you will actually be billed 250.00, an understatement of 37.53 every month for five years.

Two ways to handle it. Either ask the lender for the reducing balance equivalent, which regulated lenders in most markets are required to disclose, and enter that. Or work out the flat instalment yourself, which is easy, since it is just principal plus total flat interest divided by the number of payments, and then use the mortgage rate calculator to convert that instalment back into the real rate.

Terms that land on whole payment periods

The term goes in as years plus months, and the calculator turns that into a count of payment periods.

On monthly payments this is always exact, since every whole month is one payment. Five years and two months is 62 payments, and nothing is rounded.

On quarterly or annual payments, the calculator works in whole periods. A quarterly schedule is built from three month blocks, so a term of five years and two months is measured as twenty complete quarters. An annual schedule works the same way in twelve month blocks.

Which means the cleanest results come from matching your term to your frequency. If you are paying quarterly, express the term in whole quarters: 5 years and 3 months, or 5 years and 6 months, rather than 5 years and 2 months. If you are paying annually, use whole years.

Where a lender has genuinely written an odd term against a quarterly schedule, they will normally size the last payment differently to settle the difference. Worth asking how they intend to handle it, because a stub payment at the end is easy to be surprised by.

What sits outside the instalment

The figure this returns is the instalment against the loan itself. Several other things typically attach to a loan, and none of them are in it.

Processing and origination fees. Often a percentage of the loan, taken up front or deducted from the amount you receive. If a fee is deducted at disbursal, you are repaying a loan larger than the cash that reached you, and your real cost is higher than the quoted rate.

Insurance. Credit life cover, or comprehensive insurance on a financed vehicle, is frequently a condition of the loan and billed alongside it.

Documentation, valuation and legal charges. Especially on anything secured against property.

Late payment charges. Not a planned cost, but worth knowing the size of before you need to.

The useful discipline is to ask the lender for the total amount repayable including every charge, then compare that against the total this calculator gives you. The gap is the true cost of the fees, and it is a much harder number to argue with than a list of line items.

Questions people ask

What kind of interest rate should I enter?

A reducing balance rate, meaning one where interest is charged on the outstanding amount. If your lender quoted a flat rate, this calculator will understate your instalment considerably, because a flat rate charges interest on the full original amount for the whole term.

How do I convert a flat rate to a reducing balance rate?

As a rough guide, multiply by about 1.8. A 10 percent flat rate is close to 17.3 percent reducing, and 12 percent flat is around 21 percent. For an exact figure, work out the flat instalment and run it through the mortgage rate calculator, which solves for the rate.

Does it matter how often I pay?

Yes. On 10,000 at 10 percent over five years, paying annually rather than monthly costs an extra 441.64 in interest, because the balance sits unreduced for longer between payments.

Are fees included in the instalment?

No. Processing charges, insurance, documentation and valuation fees all sit outside it. Ask the lender for the total amount repayable including charges and compare that against the total shown here.

What if my term is not a whole number of payment periods?

On monthly payments any whole number of months works exactly. On quarterly or annual schedules the calculator works in complete periods, so matching the term to the frequency gives the cleanest result.

Can I use this for a loan in another currency?

The arithmetic is the same in any currency. The results are labelled in rupees, but feed it dollars or pounds and the numbers returned are correct in whatever units you entered.

What if I know the payment and want to know how long?

That is the loan payoff calculator, which takes an amount, a rate and a payment and tells you how many payments it takes. Between the two you can approach a loan from either end.

Should I take a longer term for a smaller instalment?

It lowers what leaves your account each month and raises what you pay in total, because the money is borrowed for longer. Run both terms here and compare the instalment against the total before deciding.

References

The instalment formula is the standard amortisation relation for a level annuity, under which the loan amount equals the present value of the payments, as set out in university financial mathematics materials for the actuarial syllabus. The treatment of a quoted annual rate as a periodic rate multiplied by the number of periods in a year, and the actuarial method under which the unpaid balance is increased each period by the finance charge earned and reduced by the payment made, follow Regulation Z, which publishes its equations so they can be used to program calculators.

1. J. Robert Buchanan, Millersville University, Loan Repayment, MATH 372 Financial Mathematics I. https://sites.millersville.edu/rbuchanan/math372/LoanRepayment-handout.pdf
2. Miguel A. Arcones, Binghamton University, Manual for SOA Exam FM, Chapter 4: Amortization and Sinking Funds, Section 4.1 Amortization Schedules. https://people.math.binghamton.edu/arcones/exam-fm/sect-4-1.pdf
3. Consumer Financial Protection Bureau (CFPB), Regulation Z, Appendix J to Part 1026: Annual Percentage Rate Computations for Closed-End Credit Transactions. https://www.consumerfinance.gov/rules-policy/regulations/1026/j/
4. Consumer Financial Protection Bureau (CFPB), Regulation Z, § 1026.22 Determination of Annual Percentage Rate. https://www.consumerfinance.gov/rules-policy/regulations/1026/22/