An EMI is the same amount every month — but inside each payment, the split between principal and interest changes dramatically. In the early months, most of your payment is interest; in the later months, most is principal — and this is the specific mechanism that makes making extra payments early in a loan far more valuable than making the same extra payment later
The previous articles on this site covered EMI basics, reducing total loan cost, mortgage amortisation, business finance structures, and refinancing breakeven. This article addresses amortisation schedule mechanics — specifically how the principal-interest split changes over a loan's life, why extra payments early save disproportionately more than extra payments late, and how to read an amortisation table.
The amortisation mathematics: why the split changes
The EMI formula produces a fixed payment amount. The interest portion of each payment is calculated on the outstanding principal balance — which decreases each month as you pay down principal.
Month 1 of a 20-year, £200,000 mortgage at 5% annual interest (≈0.417% monthly):
- Interest: £200,000 × 0.00417 = £833
- EMI: approximately £1,320 (calculated from the formula)
- Principal: £1,320 − £833 = £487
- Remaining balance: £200,000 − £487 = £199,513
Month 2:
- Interest: £199,513 × 0.00417 = £831 (slightly less — on a lower balance)
- Principal: £1,320 − £831 = £489 (slightly more)
- Remaining balance: £199,024
This continues across 240 months. By month 120 (year 10, halfway through):
- Outstanding balance: approximately £126,000
- Interest portion: £126,000 × 0.00417 = £526
- Principal portion: £1,320 − £526 = £794
By month 200 (year 16.7):
- Outstanding balance: approximately £50,000
- Interest portion: £209
- Principal portion: £1,111
The EMI is always £1,320. But what that £1,320 buys you changes dramatically — early payments are mostly interest rent; later payments are mostly principal reduction.
Why early extra payments save disproportionately more
If you make an extra £5,000 principal payment in month 6 of the above mortgage:
The outstanding balance drops by £5,000 immediately. Every subsequent interest charge is calculated on a balance that's £5,000 lower. Over the remaining 234 months, this £5,000 reduction in balance saves approximately:
£5,000 × 0.00417 × remaining months of interest exposure = roughly £3,900 in future interest
(This is a simplified estimate; the actual saving is the present value of reduced future interest payments across the loan's life.)
If you make the same £5,000 extra payment in month 180 (year 15):
- The remaining balance is approximately £74,000
- Only 60 months remain
- The interest saved: £5,000 × 0.00417 × 60 months exposure = approximately £1,250
The same £5,000 saves £3,900 in early months vs £1,250 in later months — not because the interest rate changed, but because there are fewer remaining months for the reduced balance to generate interest savings.
The "making extra payments" decision framework
Extra payments to a mortgage are a guaranteed, tax-free return equal to the mortgage interest rate. If your mortgage is at 5%, an extra principal payment earns a guaranteed 5% annual return (in interest savings) — compared to savings accounts, government bonds, or other low-risk investments.
Versus investing extra cash: if you can earn a higher after-tax return by investing than your mortgage interest rate, investing may be preferable — but this comparison requires honest risk assessment. The mortgage saving is guaranteed; investment returns are not.
Practical considerations:
- Check for early repayment charges (ERCs) on fixed-rate mortgages — many UK fixed-rate mortgages permit overpayments of 10% of the outstanding balance per year without penalty
- Maintain adequate emergency fund before making large extra payments — illiquid equity in your property is worth less than accessible cash in an emergency
- Consider tax treatment — in jurisdictions where mortgage interest is tax-deductible (US, some others), the effective interest rate is reduced by the tax benefit, which changes the investment vs overpayment comparison
Balloon loans and bullet repayment: alternatives to amortisation
Not all loans fully amortise. Some loan structures separate interest and principal repayment:
Interest-only loans: only interest is paid during the loan term; the full principal is repaid at the end. Common for some investment property mortgages and commercial real estate. No principal is being built; the full original amount is owed at maturity.
Balloon loans: regular payments (often small) are made during the term, but a large "balloon" principal payment is due at the end. The borrower must refinance or sell the asset to repay the balloon. Common in commercial finance.
The EMI amortisation structure (equal payments, each containing interest + principal, with the balance reducing to zero by the end) is the most common for consumer lending — mortgages, car loans, personal loans — because it provides predictable payment amounts and guaranteed payoff at term end.
How to use the EMI Calculator on sadiqbd.com
- Calculate your EMI for any combination of principal, rate, and tenure — the foundation for any loan assessment
- Explore the amortisation table if available in the tool — see how the principal-interest split evolves over the loan life, and how much total interest you'll pay vs principal over the full term
- Model extra payments: reduce the principal by the extra payment amount and recalculate — the new EMI (or the reduced tenure at the original EMI) shows the concrete benefit of the extra payment
Frequently Asked Questions
Why does the total interest on a long mortgage often exceed the original loan amount? Because interest compounds over time and the balance reduces slowly in early years. A £200,000 mortgage at 5% over 30 years results in total payments of approximately £386,500 — meaning you pay £186,500 in interest, nearly as much as the original loan. This isn't an anomaly or a sign of predatory lending; it's the mathematical result of interest being charged on the outstanding balance over 30 years. Reducing the term (30 years to 20 years) dramatically reduces total interest paid — though it increases the monthly payment. This is the core trade-off the previous "three levers" article covered.
Is the EMI Calculator free? Yes — completely free, no sign-up required.
Try the EMI Calculator free at sadiqbd.com — calculate monthly loan payments and see the full amortisation schedule for any loan.
