Interest Calculator — Simple Interest
Enter a principal, an annual rate, and a time period and get total interest, future value, and a full year-by-year breakdown with charts — instantly.
Simple Interest Calculator
I = P × R × T · A = P + I
ENTER YOUR VALUES
TIME UNIT
Future Value
$13,000
$10,000 @ 6% for 5 years
$3,000
Total Interest
6.0%
Effective Rate
$10,000
Principal
$3,000
Total Interest
$13,000
Future Value
30.0%
Interest / Principal
Component Breakdown
- Principal (76.9% of total)
- $10,000
- Total Interest (23.1% of total)
- $3,000
- Future Value (Total)
- $13,000
📊 Principal vs Interest Breakdown
⏱️ Rule of 72 — Time to Double
12.0 yrs
At 6% annual rate, your money doubles approximately every 12.0 years.
📅 Year-by-Year Accumulation Schedule
| Period | Opening Balance | Interest Earned | Closing Balance |
|---|---|---|---|
| Year 1 | $10,000 | $600 | $10,600 |
| Year 2 | $10,600 | $600 | $11,200 |
| Year 3 | $11,200 | $600 | $11,800 |
| Year 4 | $11,800 | $600 | $12,400 |
| Year 5 | $12,400 | $600 | $13,000 |
💡 Simple Interest Tips
For long-term savings, compound interest grows faster — see the Compound Interest Calculator.
Most bank accounts, mortgages, and credit cards actually use compound interest, not simple.
Simple interest is commonly used for short-term loans, bonds, and treasury bills.
For loan repayment calculations with amortization, use the Loan Calculator.
This calculator computes simple interest only. Most real-world financial products (mortgages, credit cards, savings accounts) compound interest. Results are estimates for planning purposes.
What Is Simple Interest?
Simple interest is calculated only on the original amount you put in or borrowed — never on interest that has already accumulated. That predictability is exactly why it's the standard for short-term loans, many bonds, and treasury bills. The formula is I = P × R × T, where P is principal, R is the annual rate as a decimal, and T is time in years — and the future value (total amount) is A = P(1 + RT). For anything that compounds instead — most savings accounts, credit cards, and mortgages — see our compound interest calculator and loan calculator.
Simple Interest Examples
| Principal | Rate | Time | Interest | Future Value |
|---|---|---|---|---|
| $5,000 | 4% | 3 years | $600 | $5,600 |
| $10,000 | 6% | 5 years | $3,000 | $13,000 |
| $25,000 | 8% | 2 years | $4,000 | $29,000 |
| $1,000 | 5% | 6 months | $25 | $1,025 |
| $15,000 | 7.5% | 90 days | $277.40 | $15,277.40 |
Simple vs Compound Interest
| Period | Simple ($10K @ 6%) | Compound (Monthly) | Difference |
|---|---|---|---|
| 1 year | $10,600 | $10,617 | $17 |
| 5 years | $13,000 | $13,489 | $489 |
| 10 years | $16,000 | $18,194 | $2,194 |
| 20 years | $22,000 | $33,102 | $11,102 |
| 30 years | $28,000 | $60,226 | $32,226 |
The Rule of 72
A quick shortcut to estimate how long it takes money to double at a given rate: divide 72 by the annual rate. It's built around compound interest, so treat it as a rough approximation rather than an exact figure for simple interest.
| Interest Rate | Years to Double |
|---|---|
| 2% | 36 years |
| 4% | 18 years |
| 6% | 12 years |
| 8% | 9 years |
| 10% | 7.2 years |
| 12% | 6 years |
— FAQ