Loan Interest Calculator

Calculate total interest, monthly payment, and the full cost of any loan.

📖 What is the Loan Interest Calculator?

The loan interest calculator shows you the total interest cost of any loan - the amount you pay over and above the principal borrowed. This is the most important number to understand before taking any loan, yet most borrowers focus only on the monthly EMI (Equated Monthly Instalment) without realising how much interest accumulates over the full tenure.

Consider a ₹5 lakh personal loan at 14% for 5 years. The EMI is ₹11,634 - manageable. But multiply that by 60 months: total paid = ₹6,98,040. Total interest = ₹1,98,040. You pay nearly 40% extra on top of the principal. This calculator makes that cost visible upfront.

The calculator supports three interest calculation methods. Reducing balance (used by all banks for home loans, car loans, and most personal loans): interest is calculated on the outstanding principal, which reduces with each EMI. Flat rate (used by some dealer financing and older loan products): interest is calculated on the original principal throughout, making it significantly more expensive. Simple interest: like flat rate but occasionally used for short-term loans. For flat rate loans, the calculator also shows the effective annual rate - the true interest rate - which is typically 1.7–1.9× the stated flat rate.

📐 Formula

Reducing Balance (EMI):

r = Annual Rate ÷ 12 ÷ 100

EMI = P × r × (1+r)^n ÷ ((1+r)^n − 1)

Total Interest = (EMI × n) − P

Flat Rate:

Total Interest = P × Rate × (Tenure in years)

EMI = (P + Total Interest) ÷ n months

Effective Rate ≈ 2 × 12 × Interest ÷ (P × (n+1))

Simple Interest:

Interest = P × Rate × Time (years) ÷ 100

📖 How to Use This Calculator

Select interest type: Reducing Balance, Flat Rate, or Simple Interest.

Enter the loan amount, annual interest rate, and tenure (years + months).

Click Calculate - total interest, monthly payment, total paid, and effective rate appear.

💡 Example Calculations

Example 1 - ₹10 lakh home loan, 8.5%, 20 years (reducing balance)

r = 8.5/12/100 = 0.007083 | n = 240

EMI = 10,00,000 × 0.007083 × (1.007083)^240 ÷ ((1.007083)^240 − 1) = ₹8,678/month

Total paid ≈ ₹20,82,776 | Total interest ≈ ₹10,82,776

Try this example →

Example 2 - ₹2 lakh car loan, 10% flat rate, 3 years

Interest = 2,00,000 × 10% × 3 = ₹60,000

Total = ₹2,60,000 | Monthly = ₹7,222 | Effective rate ≈ 19.46%

Try this example →

Frequently Asked Questions

How do banks calculate interest on a loan in India?+

Indian banks (regulated by RBI) are required to use the reducing balance method for all loan EMI products. Under this method, interest is charged only on the outstanding principal after each payment, so your effective interest cost decreases over time as you repay. Some informal lenders and older hire-purchase products quote flat rates, which are significantly more expensive - a 10% flat rate is equivalent to roughly 18–19% on a reducing balance basis.

How is EMI calculated on a loan?+

EMI = P × r × (1+r)^n / ((1+r)^n − 1), where P = principal, r = monthly interest rate (annual rate ÷ 12), n = tenure in months. This is the standard reducing balance formula used by banks. Use the EMI Calculator for full amortization schedules.

What is the total cost of a loan?+

Total cost = (Monthly EMI × Total months) + Processing fee + Prepayment penalties + Insurance (if any). Many borrowers only focus on the EMI amount, ignoring total interest paid. The total interest on a 20-year home loan can equal or exceed the original principal.

How does prepayment reduce loan cost?+

Prepayment reduces the outstanding principal, directly reducing future interest. Since interest accrues on the outstanding balance, early prepayments have the most impact. Many banks allow annual prepayment up to 25% of outstanding principal without penalty.

What is a good interest rate for a personal loan in India?+

Personal loan rates in India typically range from 10.5% to 24% per annum, depending on your credit score, income, and lender. Banks (SBI, HDFC, ICICI) offer rates from 10.5–18%. NBFCs and fintech lenders may go up to 30%+. A credit score above 750 gets significantly better rates.

How much total interest do I pay on a 20 lakh loan at 9% for 15 years?+

On a 20L home loan at 9% per annum for 15 years (180 months), the EMI is approximately 20,285. Total amount paid = 20,285 x 180 = 36.51L. Total interest paid = 36.51L - 20L = 16.51L. This means you pay 82.5% of the original loan amount as interest. Reducing the tenure to 10 years raises EMI to 25,350 but cuts total interest to 10.4L - saving 6.1L.

What does APR mean and how is it different from the interest rate?+

APR (Annual Percentage Rate) is the true annual cost of a loan, including the interest rate plus fees like processing charges, insurance, and other costs expressed as a yearly percentage. The nominal interest rate only reflects the cost of borrowing the principal. RBI requires Indian banks to disclose the Annualised Percentage Rate so borrowers can compare loans accurately. A loan with a lower interest rate but high processing fees may have a higher APR than a loan with a slightly higher rate and no fees.

How does a prepayment affect total loan interest paid?+

A prepayment directly reduces outstanding principal, which shrinks the interest charged in all subsequent periods. For example, prepaying Rs 1 lakh on a 20L home loan at 9% with 10 years remaining saves approximately Rs 52,000 in total interest and shortens the tenure by about 8 months. The earlier in the loan tenure you prepay, the greater the interest savings since more future periods benefit.

What is the difference between APR and interest rate?+

Interest rate is the cost of borrowing the principal as a percentage. APR (Annual Percentage Rate) includes the interest rate plus all fees (processing fee, insurance, etc.) expressed as an annual rate. APR gives the true cost of a loan. In India, the RBI mandates disclosure of the Annualised Rate/APR to prevent hidden fee exploitation.

What is the reducing balance method of interest calculation?+

In the reducing balance (diminishing balance) method, interest is calculated on the outstanding principal after each payment. As you repay, the principal reduces, so interest charges decrease each period. This is the standard method for home loans, car loans, and personal loans. The flat rate method calculates interest on the original principal throughout - it appears lower but results in a much higher effective rate.

🔗 Related Calculators

What is the difference between flat rate and reducing balance interest?

Flat rate: interest is calculated on the original principal throughout the loan. Reducing balance: interest is calculated on the outstanding principal, which decreases with each payment. Reducing balance is cheaper. A 10% flat rate equals approximately 18–19% effective annual rate. Always ask your lender which method they use.

How is EMI calculated on a loan?

What is the total cost of a loan?

How does prepayment reduce loan cost?

What is a good interest rate for a personal loan in India?

How much total interest do I pay on a 20 lakh loan at 9% for 15 years?

What is the difference between APR and interest rate?

What is the reducing balance method of interest calculation?

📌 Quick Tips

💡Even a 0.5% reduction in interest rate saves significantly over a long tenure. On a ₹50 lakh home loan at 8.5% vs 9% over 20 years, you save over ₹3 lakh in interest.

💡Making one extra EMI payment per year (13 EMIs instead of 12) reduces a 20-year home loan tenure by about 3–4 years and saves substantial interest.

💡Check whether the interest is calculated on reducing balance (most bank loans) or flat rate (some dealer finance). Flat rate of 10% is actually ~18–19% effective annual rate.

💡For best accuracy, use decimal values rather than fractions for non-integer inputs.

💡The FAQ section below answers the most common questions about this topic.