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This simple interest calculator calculates interest between any two dates. Per simple interest is "interest payable only on the principal". Interest is never earned or collected on previous interest. More below...»

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Related: Compound Interest Calculator

Simple interest is the interest calculation method that is least beneficial to savers and the most beneficial to borrowers. But note, if payments on a debt are paid as frequently as the compounding and the payment covers the interest due, then even if the terms of the loan call for compounding, there will be no impact on the total amount paid because at no point will there be any unpaid interest.

Related: U.S. Rule Loan & Negative Amortization

When the terms of a debt call for a simple interest calculation, if a payment does not cover the interest due, the unpaid interest must be tracked separately from the unpaid principal balance (also known as the US Rule). We believe that our Time Value of Money Calculator is the only online financial calculator that gives users this option and creates a schedule that shows the unpaid interest balance.

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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! :)

46 thoughts on “simple-interest-calculator

  1. I found this today through need and it did exactly what I wanted it to do. It was very easy to work out and use. Good work.

  2. Bank staff wouldn’t tell me how to compare income from higher-rate fixed term deposit (of say $2000) with income from lower compounding rate in online account. Eventually compounded income has to catch up – but in 3 or 30 years? Makes it hard to decide which a/c to put your money in.
    Haven’t tried a test run on your website yet.

  3. Do you have or know of a calculator I can use to calculate simple/balloon interest for multiple loan amounts with the same interest rate that are all invested into the same investment on multiple dates but all get paid off on the same single date? I am a builder and we often borrow money from private investors for the same project. For example, Investor Karl gives me $300k on 2/1/2016 to purchase the investment property/house & to have some initial working capital. When the $300k is all used up, I borrow another $100k from Investor Karl on 6/15/2016. When that is used up, I borrow another $100k from Investor Karl on 12/1/2016. I need just $50k more to finish up renovating or building the home, so I borrow $50k more from Investor Karl on 2/1/2017. ALL of the loans are at a standard 8% interest rate with a balloon interest payment & all principle paid back at the same time upon closing the sale of the subject renovated or new home, which let’s say is happening tomorrow, 4/1/2017. I owe Karl a check for $550k to return all loans immediately after closing on 4/1/2017. To figure out the check I owe Karl for interest on his multiple loan amounts starting on multiple dates I enter into your simple interest calculator each start date (which varies), each loan amount (which varies), and the interest rate (which remains the same– 8% in this case) & end date (which remains the same– 4/1/2017 in this case) 4 separate times to calculate the interest on the 4 loans and then I write them down and add them up. This example is pretty easy, but on projects where I may have 18 different loan amounts on 18 different dates it gets time consuming to do 18 different interest calculations and add them all up in the end for a final total interest figure. If you had a calculator that would allow a borrower or investor to calculate total simple interest owed on multiple loan amounts on varying dates over time to be paid back all on the same day (upon a closing), that would be sweet!

    • Hi Jon, this calculation can easily be done by the Ultimate Financial Calculator on this site. Scroll down the page and there is a list of financial calculations. Check them out. Everyone should look at #1 to get an overview of how the calculator works. Then you’ll be most interested in:

      11. Construction Loan
      Generally a short term loan with multiple borrows

      And I’m not sure from your example, if you’ll need this one or not. You might if you make periodic interest only payments.

      14. Interest Only Loan
      Initial series of interest only payments

      Basically what you’ll be doing is entering the "investment" you mention as "loans". The final line will be an "Unknown" payment amount on the date you expect to pay it back. The calculator will calculate accrued interest and principal due.

      Please let me know how this works for you.

  4. Please consider an update to the functionality of the date ranges. If I have to change just the month, I have to delete the whole thing. I wish I could just click and change specifically what I want. Also, remove the requirement to add a 0 before a month (05/01/2017). Other programs I use requiring me to enter a date range are more user friendly. This one has a learning curve for me and I do use it often for me job.

    Thank you for your consideration.

    • Hi JT, sorry not to reply yesterday. Time just got away from me.

      No doubt about it, date entry has caused users (and me) more headaches than anything else on this site. I am a bit confused as to how you are entering or changing dates. Do you want to type a date or do you want to use the pop-up calendar?

      If you want to type dates, do not try to edit them. When you tab to a date input, the date will be selected. Though it would seem to be faster to edit a date, in fact, typing 8 numbers is faster than trying to use a cursor key (which are blocked) and moving the input point a couple of digits, then use delete or backspace and then finally typing a month. (Or alternatively, taking your hand off the keyboard and using the mouse to click on the month part say and then edit it).

      So, if typing, and if you’re in the US, just tab to a date, and type:


      for today. Don’t type the date part separators even.

      If you want to change the date with the mouse, click on the calendar. If you want to change the month only, after the calendar opens, click in the top center on the current month and the calendar changes to month display. Select the month. Click the date again and the calendar will close. So, by my count, it takes 3 clicks of the mouse, if you want to use the calendar, to change to any month in the current year.

      Note the image of the calendar to the right of the calculator is attempting to get usage across.

      About dropping the ‘0’ in the date. That makes the code for handling dates a lot more complex. Having a date that is typed in always be 8 digits reduces complexity by many time, especially when supporting international date conventions.

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