Simple Interest
Simple interest is computed on the amount of the principal of a loan. That principal is multiplied by the rate of interest; the resulting figure is then multiplied by the time over which the loan will be repaid.
Simple Interest on a $100 Loan
| Time | 5% | 6% | 7% | 8% | 9% | 10% | 15% | 20% |
| 1 month | .4167 | .5000 | .5833 | .6667 | .7500 | .8333 | 1.2500 | 1.6667 |
| 6 months | 2.5000 | 3.0000 | 3.5000 | 4.0000 | 4.5000 | 5.0000 | 7.5000 | 10.0000 |
| 12 months | 5.0000 | 6.0000 | 7.0000 | 8.0000 | 9.0000 | 10.0000 | 15.0000 | 20.0000 |
| 24 months | 10.0000 | 12.0000 | 14.0000 | 16.0000 | 18.0000 | 20.0000 | 30.0000 | 40.0000 |
| 36 months | 15.0000 | 18.0000 | 21.0000 | 24.0000 | 27.0000 | 30.0000 | 45.0000 | 60.0000 |
Compound Interest
Compound interest is computed by multiplying the sum of the principal and the accrued interest by the rate of interest. This calculation must be refigured each time the principal is compounded. To determine the approximate number of years it will take for the principal to double, divide the interest rate percent into 72.
Compound Interest on $100 Principal, Compounded Annually
| Time | 5% | 6% | 7% | 8% | 9% | 10% |
| 6 months | 2.50 | 3.00 | 3.50 | 4.00 | 4.50 | 5.00 |
| 1 year | 5.00 | 6.00 | 7.00 | 8.00 | 9.00 | 10.00 |
| 2 years | 10.25 | 12.36 | 14.49 | 16.64 | 18.81 | 21.00 |
| 3 years | 15.76 | 19.10 | 22.50 | 25.97 | 29.50 | 33.10 |
| 4 years | 21.55 | 26.25 | 31.08 | 36.05 | 41.16 | 46.41 |
| 5 years | 27.63 | 33.82 | 40.26 | 46.93 | 53.86 | 61.05 |