Simple Interest Calculator — I = P × R × T
Solve for any variable in the simple interest formula — interest earned, principal, rate, or time — with a period-by-period schedule and a side-by-side simple-vs-compound comparison.
I = P × R × T
Simple Interest
A = P + I
Future Value
Simple Interest Calculator
I=P×R×T · A=P+I
FIND:
ENTER VALUES
INTEREST (I)
$3,000.00
I = $10,000.00 × 6.00% × 5.0000yrs = $3,000.00
Principal
$10,000
Future Value
$13,000
Interest / Principal
30.0%
$10,000
Principal
$3,000
Interest (I)
$13,000
Future Value (A)
30.0%
Rate × Time
Formula Applied
I = P × R × T
I = $10,000.00 × 6.00% × 5.0000yrs = $3,000.00
Principal vs Interest
⚖️ Simple vs Compound Interest — Same Inputs
Simple Interest
- Interest Earned
- $3,000
- Future Value
- $13,000
- Total Return
- 30.0%
Compound (Monthly)
- Interest Earned
- $3,489
- Future Value
- $13,489
- Total Return
- 34.9%
Compound interest earns $489 more than simple over 5.0 years.
Year-by-Year Breakdown
| Period | Opening Balance | Interest Earned | Closing Balance | Cumulative Interest |
|---|---|---|---|---|
| Year 1 | $10,000.00 | $600.00 | $10,600.00 | $600.00 |
| Year 2 | $10,600.00 | $600.00 | $11,200.00 | $1,200.00 |
| Year 3 | $11,200.00 | $600.00 | $11,800.00 | $1,800.00 |
| Year 4 | $11,800.00 | $600.00 | $12,400.00 | $2,400.00 |
| Year 5 | $12,400.00 | $600.00 | $13,000.00 | $3,000.00 |
The Simple Interest Formula Explained
Simple interest is calculated using one straightforward formula: I = P × R × T. Here, I is the interest earned or owed in dollars, P is the principal — the original amount borrowed or invested, R is the annual interest rate written as a decimal (6% becomes 0.06), and T is time in years. The total amount after interest is A = P + I, which also equals P(1+RT). Because the relationship is linear, you can rearrange the formula to solve for any single variable once you know the other three — that's what the four solve-for buttons above do. For loans and accounts that compound instead of applying a flat rate, see our compound interest calculator and loan calculator.
P = I ÷ (R × T)
Solve for principal
R = I ÷ (P × T)
Solve for rate
T = I ÷ (P × R)
Solve for time
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 Comparison
$10,000 at 6% — the gap between simple and monthly-compound interest widens every year:
| Period | $10,000 @ 6% Simple | $10,000 @ 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 |
— FAQ