![]() ![]() The interface includes a side panel that the utility refers to as a tape. Although this app can’t really do anything beyond basic arithmetic, it does have one feature I really like. Moffsoft FreeCalc ( Figure A) is a free calculator that’s designed to act as an alternative to the built-in Windows Calculator. Note: This article is also available as an image gallery and a video hosted by TechRepublic columnist Tom Merritt. Here are five choices that are worth a look. ![]() These apps, many of which are freeware, often provide functionality that doesn’t exist in the built-in Windows tool. As handy as it is, however, plenty of other calculator apps are available. One of the built-in Windows apps I find myself using the most frequently is Calculator. Mathematical Interest Theory (Second Edition), Washington DC: The Mathematical Association of America, 2009, page 75.If the built-in Windows Calculator doesn't quite meet your needs, one of these alternatives might. Vaaler, Leslie Jane Federer Daniel, James W. T=72/R = 72/0.5 = 144 months (since R is a monthly rate the answer is in months rather than years)ġ44 months = 144 months / 12 months per years = 12 years References If you invest a sum of money at 0.5% interest per month, how long will it take you to double your investment? R = 72/t = 72/10 = 7.2% Example Calculation in Months What interest rate do you need to double your money in 10 years? If you invest a sum of money at 6% interest per year, how long will it take you to double your investment? *8% is used as a common average and makes this formula most accurate for interest rates from 6% to 10%. We can solve this equation for t by taking the natural log, ln(), of both sides,įinally, multiply both sides by 100 to put the decimal rate r into the percentage rate R: Rewriting the formula:ĢP = P(1 + r) t, and dividing by P on both sides gives us If we change this formula to show that the accrued amount is twice the principal investment, P, then we have A = 2P. Where A is the accrued amount, P is the principal investment, r is the interest rate per period in decimal form, and t is the number of periods. You can also calculate the interest rate required to double your money within a known time frame by solving for R: You can calculate the number of years to double your investment at some known interest rate by solving for t: R = interest rate per period as a percentageĬommonly, periods are years so R is the interest rate per year and t is the number of years.The formula is interest rate multiplied by the number of time periods = 72: The Rule of 72 is a simple way to estimate a compound interest calculation for doubling an investment. It also assumes that accrued interest is compounded over time. Compounding This calculator assumes the frequency of compounding is once per period. You can also input months or any period of time as long as the interest rate you input is compounded at the same frequency. Time Period in Years The number of years the sum of money will remain invested. Interest Rate The annual nominal interest rate of your investment in percent. This calculator provides both the Rule of 72 estimate as well as the precise answer resulting from the formal compound interest calculation. It is a useful rule of thumb for estimating the doubling of an investment. ![]() The Rule of 72 is a simplified version of the more involvedĬompound interest calculation. For example if you wanted to double an investment in 5 years, divide 72 by 5 to learn that you'll need to earn 14.4% interest annually on your investment for 5 years: 14.4 × 5 = 72. Divide 72 by the interest rate to see how long it will take to double your money on an investment.Īlternatively you can calculate what interest rate you need to double your investment within a certain time period. Use the Rule of 72 to estimate how long it will take to double an investment at a given interest rate. ![]()
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