Loans & Credit
Published July 9, 2026
Amortisation is the process of paying off a loan through fixed instalments where the split between interest and principal changes every month. Interest for a month is the outstanding balance times the monthly rate, and whatever is left of the payment reduces the balance. Early payments are mostly interest, later ones mostly principal, even though the payment never changes.
Ever wondered why, after a year of mortgage payments, your balance has barely moved? The answer is amortization, the schedule that governs how a loan is repaid. Understanding it reveals where your money actually goes each month and, crucially, how a few extra payments can save you a fortune in interest.
Amortization is the process of paying off a loan with a series of regular, equal payments over a set term. Each payment is the same amount, but its internal split between interest and principal changes over time. Common amortized loans include mortgages, car loans, and personal loans.
Here's the key idea: interest is charged on your current outstanding balance. At the start of the loan, the balance is at its highest, so the interest portion of each payment is large and the principal portion is small. As you chip away at the balance, the interest shrinks and more of each fixed payment goes toward principal.
The mechanics for each period:
Interest = Balance x Periodic RatePrincipal = Payment - InterestNew Balance = Balance - Principal
Imagine a $200,000 mortgage at 6% over 30 years, with a fixed monthly payment of about $1,199. Watch how the split shifts:
| Payment | Goes to Interest | Goes to Principal |
|---|---|---|
| Month 1 | ~$1,000 | ~$199 |
| Month 180 (year 15) | ~$700 | ~$499 |
| Month 360 (final) | ~$6 | ~$1,193 |
In month one, 83% of your payment is interest. By the final payment, almost all of it is principal. This front-loading of interest is exactly why early balances fall so slowly, and why it's called an amortization "curve."
Enter your loan amount, rate, and term to generate a payment-by-payment breakdown of principal, interest, and remaining balance.
Use the Loan Amortization Calculator →Because interest is charged on the balance, anything that lowers the balance faster saves you interest on every future payment. Extra payments go 100% to principal, so they punch above their weight, especially early in the loan when the balance (and therefore the interest) is highest.
On that $200,000 mortgage, adding just $100 a month to the payment can cut years off the loan and save tens of thousands in interest. The earlier you start, the bigger the effect, because you're removing principal that would otherwise accrue interest for decades.
Watch out for negative amortization, where a payment is too small to cover even the interest, so the balance actually grows. Well-structured loans avoid this.
Compute the fixed payment with the amortisation formula, then for each month multiply the current balance by the monthly rate to get the interest, subtract that from the payment to get the principal portion, and reduce the balance by that principal.
Start with the opening balance and repeat four steps each row: interest equals balance times rate, principal equals payment minus interest, new balance equals old balance minus principal, then carry the new balance forward. On a $25,000 loan at 7%, month one is $145.83 interest and $349.20 principal.
Because interest is charged on the balance outstanding, and at the start the balance is at its largest. As the balance falls, the interest portion shrinks and the principal portion grows, which is why progress feels slow in the early years.
It depends on the rate and term. On a 30 year mortgage at typical rates the crossover often falls somewhere past the halfway mark, which is why the first decade builds far less equity than people expect.
Money applied directly to principal removes every future interest charge that balance would have generated, and shortens the schedule. The earlier the extra payment lands, the more months it eliminates from the end of the loan.
When the payment is smaller than the interest due, so the shortfall is added to the balance and the debt grows despite payments being made. It appears in some deferred or minimum-payment structures and should be treated as a serious warning.
Most amortized loans reduce the balance with every payment, but negative amortization occurs when a payment is smaller than the interest accrued for that period, causing the unpaid interest to be added to the principal and the balance to actually grow over time. This can happen with certain adjustable-rate mortgages that offer a minimum-payment option below the fully accruing interest, or with deferred-payment loans like some student loans and forbearance arrangements where interest continues accruing while payments are paused. Negative amortization is a genuine trap for borrowers who don't realize it's happening, since the loan can appear "paid down" by regular payments while the actual balance owed silently increases; always check the amortization schedule for any loan with a minimum-payment or deferment option to confirm the balance is actually declining.
Every amortized loan has a specific schedule showing the principal and interest breakdown for every single payment across the full term, and lenders are generally required to provide this on request even if it isn't included by default with your loan documents. Reviewing your own schedule (rather than a generic example) matters because it shows exactly how much interest you'll pay in total if you follow the loan to term, and it lets you calculate precisely how much interest a specific extra payment at a specific point in the loan would save, rather than relying on a rough rule of thumb.
Amortization explains the whole life of your loan: why early payments feel like they barely dent the balance, and why extra principal payments are so powerful. See exactly where your money goes with the Loan Amortization Calculator, then use the Loan EMI Calculator to test how a shorter term or extra payment could save you thousands. For official guidance on this topic, see the CFPB's loan guidance.
This article is for educational purposes only and is not financial advice. See our Disclaimer.