The quick answer
On a $10,000 personal loan at 10% interest over 3 years, you'll pay roughly $1,616 in total interest — meaning you repay $11,616 in total.
But change the term to 5 years and the same loan costs you $2,748 in interest — nearly double — even though the monthly payment feels lower. That's the trap most borrowers walk into without realising it.
Real examples across common loan amounts
Here's what interest actually costs across common personal loan amounts at a typical rate of 10%:
| Loan amount | Rate | Term | Monthly | Total interest | Total repaid |
|---|---|---|---|---|---|
| $5,000 | 10% | 2 years | $231 | $538 | $5,538 |
| $10,000 | 10% | 3 years | $323 | $1,616 | $11,616 |
| $15,000 | 10% | 4 years | $380 | $3,247 | $18,247 |
| $20,000 | 10% | 5 years | $425 | $5,497 | $25,497 |
| $30,000 | 10% | 5 years | $638 | $8,245 | $38,245 |
Now watch what happens when the interest rate changes on the same $10,000 loan over 3 years:
| Interest rate | Monthly | Total interest | Extra vs 5% |
|---|---|---|---|
| 5% | $299 | $778 | — |
| 10% | $323 | $1,616 | +$838 |
| 15% | $347 | $2,480 | +$1,702 |
| 20% | $372 | $3,394 | +$2,616 |
| 25% | $398 | $4,345 | +$3,567 |
A 20% rate difference costs you an extra $3,567 on a $10,000 loan. Shopping your rate is the single most impactful thing you can do before signing.
How interest on a personal loan is calculated
Most personal loans use simple amortisation — your monthly payment is fixed, but the split between principal and interest shifts over time. Early payments are mostly interest. Later payments are mostly principal.
P = principal (amount borrowed)
r = monthly interest rate (annual rate ÷ 12)
n = total number of monthly payments (years × 12)
You don't need to calculate this manually — the TrueCostLoan calculator does it instantly.
Term vs rate: which matters more?
Both matter, but in different ways. Rate determines the cost per dollar borrowed. Term determines how long you're paying that cost.
| Scenario | Rate | Term | Total interest |
|---|---|---|---|
| Base case | 10% | 5 years | $5,497 |
| Better rate | 7% | 5 years | $3,761 (save $1,736) |
| Shorter term | 10% | 3 years | $3,231 (save $2,266) |
| Both improved | 7% | 3 years | $2,178 (save $3,319) |
Shortening the term saves more here than improving the rate — but it raises monthly payments. Use the calculator to find your own sweet spot.
How to reduce the interest you pay
1. Improve your credit score before applying
Your credit score is the biggest driver of the rate you're offered. A top-bracket score versus a mid-bracket score can mean 5–10 percentage points difference — worth thousands on a significant loan.
2. Shop at least three lenders
Rates vary dramatically between lenders for the same borrower. Checking your rate typically only triggers a soft credit pull — it won't affect your score until you formally apply.
3. Choose the shortest term you can afford
As the table above shows, term has an outsized effect on total interest. A higher monthly payment is almost always worth it for the interest saving.
4. Make overpayments when possible
Check whether your lender allows overpayments without penalty. Even occasional lump sum payments applied to principal can meaningfully reduce your total interest bill.
Calculate your own loan
Use the free calculator to see the exact interest cost for your specific amount, rate, and term before you sign.