How do you learn loan amortisation quickly and correctly? Start with what happens inside one repayment. When you borrow money and repay a reducing-balance loan over time, a payment can cover interest for the period and reduce the amount still owed. An amortisation schedule shows this process payment by payment. You do not need to memorise the full loan formula on day one. In this eduKateSG Finance Quick Notes lesson, you will learn four useful words, calculate the first two rows of an imaginary loan and understand why the balance can fall slowly even when the regular instalment seems large.
- Principal: the amount borrowed or still owed, excluding separately calculated interest.
- Interest: the lender’s charge under the loan terms.
- Instalment: the amount paid on the scheduled date.
- Amortisation schedule: a table showing interest, principal repaid and remaining balance.
- Correct order: calculate interest, subtract it from the payment, then reduce principal.
- Real-world check: contracts may include fees, rate changes and different interest rules.
Teaching paragraph 1 — learn the difference between payment and principal reduction. When a person pays S$200 into a loan account, it does not always reduce the loan balance by S$200. Part may cover interest that arose since the preceding repayment, and other contract charges may apply. In a straightforward interest-bearing reducing-balance loan, the principal reduction is the payment minus interest for that period, assuming there are no additional charges or adjustments. This distinction explains why the full monthly payment is not the same thing as the increase in home equity or the decline in debt.
Teaching paragraph 2 — calculate the first month. Imagine a simplified S$1,000 loan where interest is exactly 1% of the opening balance each month, payments are made at month-end, and no fees or new borrowing occur. The first month’s interest is 1% of S$1,000, or S$10. If the instalment is S$200, then S$10 pays interest and S$190 reduces principal. The new outstanding balance is S$1,000 − S$190 = S$810. You can calculate this step without a complicated tool: find the interest, subtract it from the instalment, then subtract the remainder from the balance.
Teaching paragraph 3 — repeat with the smaller balance. In month two, calculate 1% of S$810, which is S$8.10 in interest. The S$200 payment now reduces principal by S$200 − S$8.10 = S$191.90. The new balance is S$810 − S$191.90 = S$618.10. With the same payment and constant periodic rate, the interest part became smaller while the principal part became larger. That is the learning pattern behind a typical level-payment amortising loan. The example shows only two rows, not a full loan offer or a claim that S$200 is the correct instalment for a particular loan term.
The Three-Step Repayment Method
- Step 1: calculate the period’s interest under the stated loan method.
- Step 2: find principal repaid = payment − interest, assuming no other charges.
- Step 3: calculate new balance = opening balance − principal repaid.
Keep the units consistent. A monthly periodic interest rate belongs with one month of interest; an advertised annual rate cannot simply be dropped into a monthly calculation without understanding the contract’s conversion method. A real loan may accrue interest daily, change its rate or charge fees. Always compare your teaching calculation against the official statement.
Your First Two Amortisation Rows
- Opening loan balance, month 1: S$1,000.00.
- Month 1 interest at 1%: S$10.00.
- Month 1 payment: S$200.00; principal reduction: S$190.00.
- Opening loan balance, month 2: S$810.00.
- Month 2 interest at 1%: S$8.10.
- Month 2 payment: S$200.00; principal reduction: S$191.90.
- Closing loan balance after month 2: S$618.10.
The sum of principal reductions is S$381.90. The two payments total S$400, with S$18.10 going to interest. Check the arithmetic another way: S$1,000 + S$18.10 − S$400 = S$618.10. Both methods should agree. If they do not, look for a skipped charge, incorrect interest base or arithmetic error.
What Makes a Loan Amortising?
Amortisation means paying down the outstanding loan balance through scheduled repayments over time. A fully amortising loan is structured to pay off principal and interest by the end of the agreed term if its assumptions and payment requirements are met. Some loans allow variable rates or irregular payments; others have a balloon payment left at the end. Do not assume every loan with a monthly instalment follows the same pattern. The lender’s schedule shows what the payments are intended to do.
Why Early Payments Can Contain More Interest
At the start of a long reducing-balance loan, outstanding principal is large, so interest calculated on that balance may also be large. As principal is repaid, interest generally falls if the periodic rate stays the same. Under a typical level-payment fixed-rate arrangement, that frees more of each unchanged instalment to reduce principal. It is not a mysterious fee charged only in the first years; it is a consequence of calculating interest on a larger balance earlier. Exact amounts depend on the loan terms.
What Changes When the Rate Changes?
In a floating-rate loan, the interest cost may change. Depending on the agreement, instalments may be recalculated, the repayment period may change or other terms may apply. The original payment table may then stop matching the new arrangement. Check when rates are reviewed, what benchmark applies and how the lender notifies you. Never treat an old illustration as a guaranteed repayment forecast.
A Shorter Loan Versus a Longer Loan
A longer term often reduces the required monthly instalment for an otherwise comparable amortising loan, because repayment is spread over more periods. But with the same rate and no other changes, the borrower will usually pay more total interest over the longer period. A shorter loan can cost less interest overall but demand larger regular payments. The right fit cannot be found by comparing interest totals alone: required cash flow and the ability to meet essential needs matter too.
What About Early Repayment?
Extra principal repayments may reduce the balance earlier, which can reduce future interest under some reducing-balance arrangements. But some loans impose prepayment fees, lock-in periods or other conditions. The lender might reduce the term, recalculate the instalment or handle extra payments according to particular instructions. Before paying extra, read the contract and confirm how the payment will be applied. A spreadsheet cannot override the lender’s agreement.
Negative Amortisation: A Warning Sign
If a payment is smaller than the interest added in a period, unpaid interest may be added to the debt, depending on the loan terms. The amount owed can then grow even though a payment was made. This is called negative amortisation. In our simplified example, if S$10 in interest is due but only S$6 is paid and unpaid interest is capitalised, debt grows by S$4 instead of shrinking. Not every short payment is handled the same way, so check the agreement and contact the lender if a payment may be missed.
How to Read a Repayment Schedule
- Find the opening principal balance for each payment period.
- Check the rate and whether interest is monthly, daily or calculated another way.
- Find the scheduled repayment amount and date.
- Identify how much goes to interest or other charges.
- Identify how much actually reduces principal.
- Check the closing balance and compare with your statement.
- Look for final instalment adjustments and separate fees.
If the numbers do not match your own record, do not assume your method or the lender’s statement must be wrong. Ask whether the payment was credited on a different day, whether a fee applied or whether the interest rate changed. A good finance learner uses the schedule to ask precise questions, not merely to copy a number.
Mistakes to Avoid
- Subtracting the entire instalment from principal without accounting for interest.
- Using the original loan amount as the interest base forever.
- Mixing annual and monthly rates without understanding the conversion.
- Assuming a lower monthly instalment always means a cheaper loan.
- Forgetting fees, floating-rate changes and prepayment restrictions.
- Treating the first two illustrative rows as a complete repayment offer.
- Ignoring a payment too small to cover the interest.
Ten-Minute Practice
- Minutes 1–2: define principal, interest, instalment and amortisation.
- Minutes 3–4: calculate 1% interest on an imaginary S$500 opening balance.
- Minutes 5–6: assume a S$100 payment and find the principal reduction.
- Minutes 7–8: calculate the new balance and next month’s interest at 1%.
- Minutes 9–10: explain why the second period’s interest is smaller if the rules remain unchanged.
Practice Answers
Month one: 1% of S$500 is S$5 interest. A S$100 payment reduces principal by S$95, leaving S$405. Month two: 1% of S$405 is S$4.05 interest. If another S$100 is paid with no other changes, principal falls by S$95.95 to S$309.05. Focus on why each number appears rather than memorising the answer.
Continue the Finance Quick Notes
Read How to Learn Debt Repayment Quickly and Correctly for the balance equation, How to Learn Effective Interest Rates Quickly and Correctly for comparing borrowing structures and How to Learn Cash Flow Quickly and Correctly to see how payment dates affect what is available.
Reliable Sources and Final Rule
The Consumer Financial Protection Bureau’s guide to mortgage amortisation explains how principal and interest shares change. See MoneySense — How Home Loans Work for Singapore home-loan considerations. This lesson is general financial education, not a loan recommendation. Remember: interest first, principal reduction second, remaining balance third.