How a Monthly Loan Payment Is Calculated
An EMI - equated monthly instalment - is a fixed payment that clears a loan over a set term. Every fixed-rate loan uses the same formula. The Loan / EMI Calculator applies it and shows the total interest.
What the formula is doing
The payment has to satisfy one condition: paying that amount every month, at that interest rate, must leave a balance of exactly zero at the end of the term. There is only one amount that does, and the formula finds it.
Three inputs decide it. The principal - what you borrow. The monthly rate - the annual rate divided by twelve. The number of payments - the term in months.
Each payment covers that month's interest on the outstanding balance first, and whatever is left reduces the principal. Because the balance falls, the interest portion falls and the principal portion grows, which is why the payment stays flat while its composition shifts. That shift is the whole mechanic, and it is what the early part of any loan is really about.
Why a longer term costs so much more
Lengthening the term lowers the payment, which is why it is offered. What it does to the total is less visible.
Borrow 20,000 over three years at 8 per cent and the payment is around 627 with roughly 2,560 in total interest. Stretch the same loan to seven years and the payment drops to about 312 - but the total interest rises to roughly 6,200. Less than half the monthly payment, nearly two and a half times the interest.
That trade is not automatically wrong. A lower payment can be the difference between manageable and not. It is simply a trade, and the total is the number lenders advertise least.
What the figure leaves out
An EMI is the loan payment. It is not the cost of the loan.
Arrangement fees, documentation charges and insurance bundled in at sale all add to what you pay and may not be inside the quoted payment. The number to compare between offers is the APR, which is meant to include the compulsory charges, rather than the headline rate or the monthly figure.
Also worth checking before signing: whether overpayment is allowed and whether it is penalised. A loan you can overpay without charge is considerably better than one you cannot, and the difference never appears in the monthly figure.
Common questions
Why is my first payment mostly interest?
Because interest is charged on the outstanding balance, and at the start the balance is at its largest. The proportion shifts as the balance falls.
Does overpaying reduce the term or the payment?
Depends on the lender, and some let you choose. Reducing the term saves more interest; reducing the payment improves monthly cash flow.
Is a fixed or variable rate better?
A judgement about your own circumstances and rate expectations rather than arithmetic, and genuinely worth discussing with a broker or adviser rather than a calculator.
What is the difference between flat and reducing-balance interest?
Flat charges interest on the original amount throughout, which costs far more for the same quoted rate. Reducing-balance is standard for most loans and is what this formula assumes.
Want to see a payment and its total interest?