What is the simple interest formula?

The simple interest formula is SI = P × R × T ÷ 100, where P = principal amount, R = annual interest rate (%), and T = time in years. Total amount = P + SI.

Simple Interest Calculator — Daily, Monthly & Yearly (SI Formula)

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Simple Interest Formula

SI = P × R × T ÷ 100

P = Principal (initial amount)
R = Annual interest rate (%)
T = Time period in years
Total Amount = P + SI

For months: SI = P × R × (M ÷ 12) ÷ 100
For days: SI = P × R × (D ÷ 365) ÷ 100

How to Calculate Simple Interest — Step-by-Step

Simple interest means interest is charged only on the original principal, never on accumulated interest. Follow these steps:

Write down your principal (P), annual rate (R) and time (T).
If time is in months, convert to years: divide by 12. If in days, divide by 365.
Apply the formula SI = P × R × T ÷ 100.
Add the interest to the principal to get the total amount.

Example (P = 100,000, R = 10%)	Calculation	Interest
2 years	100000 × 10 × 2 ÷ 100	৳20,000
6 months	100000 × 10 × 0.5 ÷ 100	৳5,000
90 days	100000 × 10 × (90÷365) ÷ 100	৳2,465.75

Daily Simple Interest

To find the interest earned per day, use: Daily Interest = P × R ÷ 36500. For example, 1,00,000 Taka at 10% per year earns ৳27.40 per day. Multiply by the number of days to get the total interest. This method is commonly used for late payment fees and short-term loans in Bangladesh.

সরল সুদ ক্যালকুলেটর (Simple Interest in Bengali)

সরল সুদ = মূলধন × সুদের হার × সময় ÷ ১০০। এখানে মূলধন (P) হলো যে টাকা জমা বা ধার করা হয়েছে, সুদের হার (R) হলো বার্ষিক শতকরা হার, এবং সময় (T) হলো বছর হিসাবে সময়। মাসকে বছরে ভাগ করতে ১২ দিয়ে ভাগ করুন এবং দিনকে বছরে ভাগ করতে ৩৬৫ দিয়ে ভাগ করুন। মোট টাকা = মূলধন + সরল সুদ। বাংলাদেশে ব্যাংকের সঞ্চয়ী হিসাবে সাধারণত বার্ষিক ৩% থেকে ৬% সুদ দেওয়া হয়।

Typical Savings & Loan Rates in Bangladesh (2026)

Account / Product	Typical Rate	Interest Type
Savings Account	3% – 6% per year	Monthly / Quarterly compound
Fixed Deposit (FDR)	5% – 9% per year	Simple or compound
Personal Loan (Banks)	9% – 16% per year	Reducing balance
Microfinance / NGO Loans	18% – 30% per year	Flat rate

Rates vary by bank and tenure. Use the calculator above to check your exact interest before borrowing.

Frequently Asked Questions

Use the formula SI = P × R × T ÷ 100, where P is the principal, R is the annual interest rate in percent, and T is the time in years. For months, divide T by 12. For days, divide T by 365.

Simple interest for days is calculated as SI = P × R × D ÷ 36500, where D is the number of days. For example, 100,000 Taka at 10% for 90 days = 100000 × 10 × 90 ÷ 36500 = 2,465.75 Taka.

Simple interest is calculated on the original principal only. Compound interest is calculated on the principal plus accumulated interest, so it grows faster over time. Bank deposits in Bangladesh typically use compound interest.

Savings account interest rates in Bangladesh typically range from 3% to 6% per year. Fixed deposit (FDR) rates range from 5% to 9% depending on the bank and tenure. Check your specific bank for current rates.

For monthly simple interest, convert months to years first: T = months ÷ 12. Then use SI = P × R × T ÷ 100. Example: 50,000 Taka at 12% for 6 months = 50000 × 12 × 0.5 ÷ 100 = 3,000 Taka.

Simple interest is interest calculated only on the principal amount, not on accumulated interest. It is commonly used in short-term loans, savings bonds and academic problems.