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This compound interest calculator calculates interest between any two dates. A dozen compounding frequencies are supported (did we miss any? :). You can also enter negative interest rates. More details below...»

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$ : mm/dd/yyyy
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Related: Rich Man, Poor Man - about the power of compounding

When interest is compounded, interest is paid on previously earned interest. If you are an investor, you want to compound interest. If you are a debtor, you want to avoid it, particularly if you ever miss a payment or a payment is not enough to cover the interest due.

You can use this online interest calculator as a:

  • loan interest calculator
  • savings interest calculator
  • daily interest calculator
  • negative interest calculator
  • investment interest calculator

As a side benefit to this calculator's date accuracy, you can use it for date math calculations. That is, given two dates, it will calculate the number of days between them or it will find the date that is "X" days from the first date.

Compound Interest Calculator Help

Enter an amount and a nominal annual interest rate.

Date Math: If you change either date, days between dates will be calculated. If you enter a positive number of days, the end date will be updated. If you enter a negative number of days the start date will be updated.

The above means you can calculate interest for a specific number of days and not worry about what the dates are. If you need to know the interest for 31 days, then enter 31 for the number of days and don't worry about the dates.

Set the compounding and days-in-year. Click "Calc". Interest and future value are calculated (FV is starting amount plus the interest.) Annual percentage yield is used for comparing investments. It is the rate institutions must quote in the US for interest bearing accounts. The holder of such an account can use the APY to compare different accounts.

Interest may be calculated based on a unit of time, say a month. This is known as "Periodic Interest" In that case, a month's interest is always the same for the same interest rate and same principal balance regardless of the length of the month. Given $10,000 principal and an interest rate of 6.75% the interest will be the same for February as it is for March. Note if you select a periodic method such as "weekly", "biweekly" etc., and if the dates enter do not equate to a number of full periods, then interest will be calculated for the fractional period by counting the days and calculating simple interest. This generally results in 1/2 a month's interest being less than 1/2 of a full month's interest when using monthly compounding.

There is also "exact day interest". Interest is calculated based on the number of days. In this case, the amount of interest will be different for February and March. Set compounding to "continuous", "daily" or "simple" for daily interest calculations.

Calendar Tip: When using the calendar, click on the month at the top to list the months, then, if needed, click on the year at the top to list years. Click to select a year, select a month and select a day. Naturally you can scroll through the months and days too. Or you can click on "Today" to quickly select the current date.

If you prefer not using a calendar, single click on a date or use the [Tab] key (or [Shift][Tab]) to select a date. Then, as mentioned, type 8 digits only - no need to type the date part separators. Also, because the date is selected, you do not need to clear the prior date before typing. If mm/dd/yyyy is selected for the date format, for March 15, 2016, type 03152016.

Related: Loan Carrying Cost: Interest Reduction Techniques

Related: What tools does the Fed have left? Part 1: Negative interest rates. (Link goes to Ben Bernanke's Blog)

The compound interest calculator has been, over the years, one of the more popular financial calculators on this site. We hope you find it useful.

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Please tell me how you use this calculator. Are you using it personally or professionally? What feature is important to you? If it didn't meet your needs, why? Your feedback will help me make improvements. Complete sentences aren't necessary! :)

33 thoughts on “compound-interest-calculator

  1. Did you make any recent changes to the site, i am no longer able to select, double click and copy any of the calculated information under “Days In Year”. This is a minor issue but i used this site a lot numerous times a day and being able to double click and copy that information saved me valuable seconds and minutes at my job, please advise.

    • Yes, in fact some changes were released early Monday. But none of the changes should have impacted this calculator. (The changes were to the Mortgage Calculator and to the schedule and a new loan calculator widget was introduced.) That’s not to say that something didn’t go wrong. I’ll have to review.

      But just to be clear, you’re saying that previously, you could click in the Days in Year input and it would be selected, and that would allow you to copy / paste the selection to another program. Do I get you? If so, I’m surprised it ever worked that way, that is, the item could be selected. Wait, I was just playing around, and I can select the text. This is what I did. I click just outside the box and dragged my mouse into the dropdown box while holding the mouse button down and the text was selected.

      I’m wondering if, in the past, you may have just missed with the click and moved the mouse and the text got selected. Is that possible?

      I really appreciate it when people take the time to comment on changes – particularly unexpected ones! That’s one of the challenges I have is trying to make changes in one place and not negatively impacting something else.

      • Thanks for your response before previously I would be able to click on the calculated interest and the future total and selected copy and then paste it on another program just today I noticed that that function is no longer available and it is very useful for the type of work I do I haven’t tried clicking around and seeing if I can select it but when I tried to do it I get the circle with the line through it and it did not allow me to select copy and paste it elsewhere

        • I’ll check, but I can select the results by clicking and dragging my mouse:

          Interest Earned:
          Future Value (FV):
          Annual Percentage Yield (APY):
          Daily Interest Rate:

          • Karl,
            I can also copy everything by clicking and dragging my mouse but up until yesterday I was able to click inside of “Interest Earned” and “Future Value” and select (either right click or Ctrl + V) only the calculated “dollar amount”. This option is no longer available. I’m sure this was just changed because I use the site probably 4 or 5 times per day.

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