📈 Simple Interest Calculator
SI = (P × R × T) / 100
Frequently Asked Questions
How do I use the Simple Interest Calculator?
Enter the Principal Amount, Annual Interest Rate, and the Time Period (choosing Years, Months, or Days), then click Calculate. You'll see the Total Amount, Interest Earned, and a breakdown of daily, monthly, and yearly interest, plus money doubling/tripling milestones and a growth projection table.
What is the formula for simple interest?
Simple Interest (SI) = (P × R × T) / 100, where P is the principal amount, R is the annual interest rate (%), and T is the time period in years. The total amount payable is Principal + Simple Interest.
What is the difference between simple interest and compound interest?
Simple interest is calculated only on the original principal amount for the entire period, so it grows linearly. Compound interest is calculated on the principal plus any interest already earned, so it grows faster over time. Use our Compound Interest Calculator to compare.
How do I calculate simple interest for months or days?
Select "Months" or "Days" as the time unit. The calculator converts the period to years (months ÷ 12, days ÷ 365) before applying the SI formula, so the annual rate is applied proportionally to the shorter period.
How long will it take to double my money with simple interest?
With simple interest, the time to reach any multiple of the principal is T = (multiple − 1) × 100 / R years. For example, at 8% per annum, doubling your money (2×) takes 100 / 8 = 12.5 years. The Money Milestones section shows this for 2×, 3×, 5×, and 10× automatically.
Is simple interest used for loans or deposits?
Simple interest is commonly used for short-term loans, certain fixed deposits, and some personal/vehicle loans. Most bank loans (like home and personal loans) and recurring/fixed deposits actually use compound interest — check our EMI Calculator or FD Calculator for those cases.
Why is the "daily interest" figure so small compared to yearly interest?
With simple interest, the total interest accrues at a constant rate throughout the period, so the daily figure shown is simply the total interest earned divided by the number of days in the period (or yearly interest ÷ 365). It doesn't grow over time the way compound interest does, since simple interest is always calculated on the unchanging original principal.
Why does the same nominal rate give a different total return for simple vs compound interest over the same period?
With simple interest, every period earns interest only on the original principal, so total interest grows linearly (R% per year of P, every year). With compound interest, each period's interest is added to the base on which the next period's interest is calculated, so growth is exponential. Over short periods (a year or two) the difference is small, but it widens significantly for longer tenures — try the same numbers on our Compound Interest Calculator to see the gap.