Simple Interest Calculator
Quickly calculate simple interest on loans, investments or financing. Find out the interest amount and the final total with an easy-to-use tool.
With simple interest, returns are always calculated on the original amount, without one period's interest earning interest in the next period — unlike compound interest. This model shows up in some short-term loans, simplified financing plans, and in calculating penalties or overdue-payment adjustments in contracts that explicitly specify "simple interest." Enter the initial amount, the interest rate, and the term to see how much interest will be paid or earned and the final total.
How to use
- Enter the initial amount of the loan, investment, or financing.
- Fill in the interest rate, choosing whether it's monthly or yearly.
- Enter the term, in months or years, and watch the result update automatically.
Worked example
A personal loan of $2,000.00 is taken out at 3% per month (simple interest), to be paid back in 8 months. The total interest is $2,000.00 × 0.03 × 8 = $480.00, and the final amount owed is $2,480.00. Notice that, unlike compound interest, that $480.00 in interest is split evenly across the 8 months ($60.00 a month) — there's no acceleration in growth over time.
Frequently asked questions
What's the simple interest formula?
Interest = Principal × Rate × Time. For example, $1,000 at 2% per month for 6 months generates $1,000 × 0.02 × 6 = $120 in interest.
What's the difference between simple and compound interest?
With simple interest, the interest amount is always calculated on the original principal. With compound interest, each period's interest becomes part of the amount that also earns interest in the next period, leading to faster growth over time.
How is a monthly rate converted to a yearly term (or vice versa)?
Since simple interest grows linearly, the conversion is direct: a rate of 2% per month equals 24% per year (2% × 12), with no compounding adjustment — unlike what happens with compound interest.
Where does simple interest show up in practice, besides loans?
It also appears in calculating contractual penalties, late-payment adjustments when a contract specifies "simple interest" (as on some installment bills), and in some very short-term, simpler fixed-income instruments.
For the same principal, rate, and term, is simple interest always lower than compound interest?
Yes, whenever the term is longer than one period (for example, more than one month, if the rate is monthly). With compound interest, each period adds previous interest to the base for the next period, so the final amount is always equal to or greater than with simple interest under the same parameters — the gap widens the longer the term.
How do I know if a contract uses simple or compound interest?
The contract usually states this explicitly in its interest clauses. If in doubt, it's worth calculating the expected amount both ways and comparing it to what's actually charged — or asking the financial institution directly, since most long-term loans and financing in practice use compound interest, not simple.