Want to know the calculation of bank loan interest?

This is how to calculate it


Who of you ever thought of calculating credit interest? Must be very little. Because usually you will count only on the amount of disbursed credit and what percentage of interest is given, and how much installments you will pay.

Even though the credit interest given by the bank turns out to have its own calculation. And it turns out again, different types. That applies to any credit, including KTA, home loans, and motor vehicle loans. Then, what's the use for you to know about the ins and outs of this interest calculation? You will be more understanding so that you are not entangled in a loan interest that is suffocating.


Calculation of Flat Interest
This flat flower is easiest to calculate. Why? Because each month the amount of installments is the same. Similarly, the principal installments and interest. Everything is calculated proportionally, adjusted to the credit tenor.

The calculation formula: Interest per month = (P x I xt) / jbP = loan principal

I = interest rate per year

t = number of years of credit period

jb = number of months in the credit period

Sample case:

Loan principal: IDR 18,000,000

Flat interest : 5% / year

Credit period: 24 months

Interest calculation: Rp. (18,000,000 X 5% X 2) / 24 = Rp. 75,000

That way, starting from the first installment until the last amount is Rp. 825,000. Consisting of principal installments of IDR 750,000 and flat interest IDR 75,000.

This effective interest is often used on long-term loans, for example on mortgages or investment loans. This type is also called the sliding rate. More days, the calculation of the portion of interest and principal loans will change even though the number of installments remains the same. Calculated based on the remaining principal debt.

And of course, the amount of interest paid is smaller than flat interest . Because the type of credit that must be repaid in the long term.

The analogy is this, the second installment will be less than the first installment. The third installment amount will be less than the second installment, and so on.

The calculation formula: Bunga = SP xix (30/360)

SP = the loan principal balance of the previous month

i = interest rate per year

30 = number of days a month

360 = number of days in a year

Sample case:

Loan principal: IDR 18,000,000

Interest: 10% / year

Credit period: 24 months

Effective interest rate for month 1 = IDR 18,000,000.00 x 10% x (30 days / 360 days) = IDR 149,940

Principal installments and 1 month interest = IDR 750,000 + IDR 149,940 = IDR 899,940

Effective 2 months interest rate = Rp. 17,250,000 x 10% x (30 days / 360 days) = Rp. 143,175

Principal installments and 2 month interest = IDR 750,000 + IDR 143,175 = IDR 893,175

From the example above, it is clear that the first and second installments differ, namely the first installment is Rp. 899,940, and the second installment is Rp. 893,175. The second installment is smaller than the first installment. (Also Read: Want to Save Money but Stay Fun? Use this Credit Card)


Almost the same as effective interest. But it is slightly modified. The interest at the beginning of the loan will look very large but then it will gradually shrink as it approaches the end of the credit period. The method of calculation is also the same as the effective interest. Well, the only difference is, the installments will remain every month.

Although the amount of interest and principal installments change according to the credit period. This is intended to facilitate customers in paying installments. In essence, the remaining credit is reduced, but the installments do not change in amount.

While according to the nature of the calculation, there are two types of interest, namely:

Fixed ( Fixed )

Even though interest rates on the market rise, this will not have an effect, as long as the credit period lasts and even though market conditions change, credit agreements agreed upon in the beginning will never change.

For example, the agreement is determined for the initial interest of 12% and remains alias there will be no change. Then until the installment period ends, the interest will remain the same at 12%.

The disadvantage of this fixed interest is that if the interest rate market is plummeting, the fixed interest paid by the customer can be said to be quite large. Examples of how to calculate interest rates are calculated using the sliding loan principal :

Loan principal: IDR 18,000,000

Interest: 12% / year

Credit period: 24 months

Month 1

Interest = 12% X IDR 18,000,000 / 12 X 1 = IDR 180,000

Loan principal = IDR 18,000,000 / 24 = IDR 750,000

1 month installment = IDR 750,000 + IDR 180,000 = IDR 930,000

Month 2

The remaining loan principal = Rp. 18,000,000 - Rp. 930,000 = Rp. 17,270,000

Interest = 12% X Rp. 17,270,000 / 12 x 1 = Rp. 172,700

2-month installments = IDR 750,000 + IDR 172,700 = IDR 922,700

So, so on the calculation method until the installments run out or paid off according to the credit period taken.

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