Knowing how to calculate interest on a loan in Nigeria will save you the stress of guessing how much you’ll repay if you borrow a loan.
Before you collect any loan in Nigeria you should know exactly how much you are going to pay back and not just how much you are borrowing.
The mistake some borrowers in Nigeria make is that, they tend to focus more on the amount they need and ignore the total cost amount they’ll pay back and when the pay back time comes, they start feeling overwhelmed.
Understanding how loan interest is calculated puts you in a position of power because with that, you can properly calculate and compare what different lenders have to offer.
With that, you can know whether the interest rate that a lender is showing you is actually cheap or expensive.
Understanding Loan Interest
Let’s first of all understand what loan interest truly implies.
Loan interest is simply the extra cost that a lender charges you in addition to the principal amount you collected and it is usually charged based on percentage.
Loan interest could be charged hourly, daily, weekly, monthly, bi-annually or annually.
So when a loan app tells you the interest rate is 5% monthly it means for every ₦100 you borrow you are going to pay an extra ₦5 on for every single month until the loan is fully repaid.
The Two Main Methods of Calculating Loan Interest in Nigeria
There are two major methods that lenders in Nigeria use to calculate the interest on your loan.
These two methods are entirely different and they produce different results even when the loan amount and interest rate look the same.
Knowing the difference between these two will save you serious money and also save you from borrowing wrongly.
Method 1: Flat Rate Interest
A flat rate interest rate implies that the amount of interest you will pay will be fixed. This means that the interest is calculated based on the original amount you borrowed and not the existing amount you are owing.
Here, the interest remains constant throughout the loan tenure and does not reduce even when the principal amount decreases with your monthly repayments.
For example, let’s say you borrowed ₦5,000 and you are to be charged ₦50 daily interest, then a long the journey you paid off ₦4,000 out of the ₦5,000, at this point you should be expecting that the interest will be calculated based on the remaining ₦1,000 balance but flat rate says no, we are still going to charge you ₦50 daily until you completely clear up all the debt.
So if it takes you let’s say the next 5 years to clear up the remaining ₦1,000, flat rate says the lender will continue charging you ₦50 daily for the 5 years until the day you completely clear it up.
Most loan apps in Nigeria calculate their interest using flat rate interest method and that is why their total repayments are always higher.
The formula for calculating flat rate interest is:
- Total Interest = Loan Amount × Flat Rate % × Time in Months/12
- Total Repayment = Loan Amount + Total Interest
Example 1:
Let’s say you borrow ₦500,000 at a flat rate of 24% per annum and you want to repay the loan over 12 months.
So it becomes;
Total Interest = ₦500,000 × 24% × 1 year = ₦120,000
Total Amount to Repay = ₦500,000 + ₦120,000 = ₦620,000
Monthly Repayment = ₦620,000 ÷ 12 = ₦51,667 per month. So you’ll be paying ₦51,667 throughout till you completely pay off the loan.
Example 2
Let’s say you borrow ₦100,000 at 3% flat rate per month for 3 months
3 months = 0.25 years (3 months ÷ 12 = 0.25 years) and 3% is the same as 0.03.
Total Interest = ₦100,000 × 3% × 3 months = ₦9,000
Total Repayment = ₦100,000 + ₦9,000 = ₦109,000
Monthly repayment = ₦109,000 ÷ 3 = ₦36,333
Observation: Flat rate is misleading because 3% per month = 36% per year flat but the APR/reducing balance is about 60-70% per annum because your debt balancing will be reducing on each monthly repayment.
Method 2: Reducing Balance Interest
Just as the name implies, reducing balance interest means that the interest will reduce as you repay part of your debt.
Here, your interest is calculated based on the outstanding balance after each repayment and not the original amount that was borrowed. So you only pay for “what you are owing”, not “what you were owing.”
Most Banks in Nigeria mostly use the reducing balance interest method and it’s the best for instalmental repayment.
The formula for reducing balance interest is:
Monthly Interest = Outstanding Loan Balance × Monthly Interest Rate
Principal Repaid = Monthly Repayment – Monthly Interest
Closing Balance = Opening Balance – Principal Repaid
Monthly Interest Rate = Annual Rate ÷ 12
Interest rate calculation Example:
Let’s say you borrowed ₦100,000 loan for 3 months at a 24% yearly interest rate which will be = 2% interest per month.
For 1 Month:
- Outstanding Loan: ₦100,000
- Interest: ₦100,000 × 2% = ₦2,000
- Principal Repaid: ₦34,336 – ₦2,000 = ₦32,336
- Closing Balance: ₦100,000 – ₦32,336 = ₦67,664
2 Month:
- Opening Outstanding Loan Balance: ₦67,664
- Interest: ₦67,664 × 2% = ₦1,353.28
- Principal Repaid: ₦34,336 – ₦1,353.28 = ₦32,982.72
- Closing Balance: ₦67,664 – ₦32,982.72 = ₦34,681.28
3 Month:
- Opening Outstanding Loan Balance: ₦34,681.28
- Interest: ₦34,681.28 × 2% = ₦693.63
- Principal Repaid: ₦34,336 – ₦693.63 = ₦33,642.37
- Closing Balance: ₦34,681.28 – ₦33,642.37 = ₦1,038.91 ≈ ₦0
Total interest paid throughout = ₦2,000 + ₦1,353.28 + ₦693.63 = ₦4,046.91
If you compare to flat rate interest on the same amount at same interest rate 2% per over the same 3 months, you will get:
Flat rate interest = ₦100,000 × 2% × 3 = ₦6,000
Reducing Balance Interest: = ₦2,000 + ₦1,353.28 + ₦693.63 = ₦4,046.91
Reducing balance rate has saved you from paying ₦1,953 extra interest.
The reducing balance method is more borrower-friendly because you only pay interest on what you still owe and not on what you’ve already repaid.
Summary of Flat Rate vs Reducing Balance
| Feature | Flat Rate | Reducing Balance |
|---|---|---|
| Interest Calculated On | Full Original Amount | Outstanding Balance Only |
| Monthly Payment | Same Every Month | Slightly Reduces Over Time |
| Total Interest Paid | Higher | Lower |
| Used By | Loan Apps Mostly | Banks and Mortgage Lenders |
| Better for Borrower | No | Yes |
Loan Interest Rate Calculator
Calculate the estimated monthly interest rate charged by a loan app or bank.
You don’t always need to waste time trying to calculate your loan interest manually. The loan calculator is a very simple tool that can help you calculate the interest rate of any loan with seconds.
How to use Loan Calculator?
To use any loan calculator simple follow these steps:
- Enter the loan amount you want to borrow
- Choose your loan duration
- Choose the repayment tenure
- Click on “Calculate Interest” and the interest and the total repayable amount will be displayed.
Loan apps like Renmoney, Carbon, FairMoney, and most many more have loan calculators on their platforms. It takes less than a minute to use this calculator.
See Also: Loan Apps With the Lowest Interest Rate in Nigeria in 2026
Frequently Asked Questions
What is the formula for calculating loan interest in Nigeria?
For flat rate, the formula to calculate the interest is: Total Interest = Principal × Rate × Duration. For reducing balance, the formula for calculating interest is: Monthly Interest = Outstanding Balance × Monthly Rate and the monthly rate is your annual rate divided by 12.
Can I calculate my loan interest manually?
Yes. You can do that using the interest rate formulas but you must first of all know the interest rate, the type of interest applied, and the tenure the loan will last.
What is the average loan interest rate in Nigeria?
Most Banks in Nigeria generally charge between 20% to 30% interest per annum on and they mostly use reducing balance interest while fintech digital loans charge between 2% to 10% monthly (24% to 120%) per annum using flat rate interest approach.
Conclusion
Calculating loan interest is very simple. You can do that using the flat rate interest formula, the reducing balance interest formula or a loan calculator.
