Why Your Repayment Method Matters
When you take out a personal loan, the repayment structure determines not just how much you pay each month, but how much interest you pay in total. Two of the most common methods are the fixed installment (flat rate) and the reducing balance (diminishing balance) approach. Understanding the difference can have a real impact on your overall borrowing cost.
Fixed Installment (Flat Rate) Method
Under the flat rate method, interest is calculated on the original principal for the entire loan term. Even as you repay the principal, the interest charge stays the same every month.
How It's Calculated
- Multiply the original loan amount by the annual interest rate
- Multiply that by the number of years
- Add the result to the principal, then divide by the total number of months
Example: A $10,000 loan at 10% flat rate over 2 years:
- Total interest = $10,000 × 10% × 2 = $2,000
- Total repayable = $12,000
- Monthly payment = $12,000 ÷ 24 = $500/month
Reducing Balance Method
Under the reducing balance method, interest is calculated on the outstanding principal each month. As you repay the principal, the interest component decreases — meaning more of each payment goes toward the principal over time.
How It Works in Practice
In early months, your payment is weighted more toward interest. As the loan matures, more goes to principal. The total interest paid is significantly lower than the flat rate method, even if the stated interest rate appears the same.
Example: A $10,000 loan at 10% reducing balance over 2 years yields a monthly payment of roughly $461/month — and total interest of approximately $1,050, compared to $2,000 under the flat rate.
Comparison at a Glance
| Feature | Flat Rate | Reducing Balance |
|---|---|---|
| Interest Basis | Original principal | Outstanding principal |
| Monthly Payment | Fixed (higher) | Fixed but lower total cost |
| Total Interest Paid | Higher | Lower |
| Simplicity | Easier to calculate | Slightly more complex |
Which Method Should You Choose?
Opt for Reducing Balance When:
- You want to minimize total interest paid
- You plan to make extra payments or repay early
- You're comparing loans and want the true cost of borrowing
Flat Rate May Appear In:
- Older loan agreements or informal lending arrangements
- Certain auto financing products
- Situations where lenders use it to make rates look lower
A Word on Early Repayment
If your loan uses reducing balance, making extra payments reduces the outstanding principal faster — directly cutting future interest charges. With a flat rate loan, early repayment savings are less straightforward and may be subject to prepayment penalties. Always check your loan agreement before making lump-sum payments.
The Bottom Line
The reducing balance method almost always results in a lower total cost of borrowing. When evaluating loan offers, ask your lender to clarify which method they use and request an amortization schedule so you can see exactly how your payments break down month by month.