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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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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.

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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93 Comments on “Simple Interest Calculator”

financial online calculator Join the conversation. Tell me what you think.
  • I understand your point, but I hardly think it makes the “site useless”. I guess it depends on whether you want to calculate the amount of interest expected for the future or confirm the amount of interest earned .

    You do know you can set the dates to whatever you want them to be, right?


    1. A user does not have to use the calendar. Just type the numbers, not even the separators. So, if the date format is mm/dd/yyyy, the user would type, for today: 03022016.

    2. Perhaps even better, if you want to use the calendar and the date is a few years back, click on the month at the top, this lists the months and the year then is at the top. Click on the year, you’ll see years where dates normally are. Pick a year, pick the month, pick the date.

    Perhaps understanding this will help to make the calculator a bit more useful for you.

    • I will also add, it would not be too difficult to change this calculator so that the end date defaults to “today’s” date when the calculator is first loaded.

      I’ll give it a month or so and we’ll see if other users care to weigh in on this. If more users prefer that option. Then it can be changed.

    • I understand what your saying, in my line of work, I’m usually calculating interest from the past through today. Thanks for your response though

      • One other thing I should have pointed out. If you open the calendar on the “End Date”, at the bottom, there is the word “Today”. Click on that. It will set the date to the current date.

  • Greetings,
    I only found your calculator recently, although from the comments I have read it appears it has been around for some time. Thanks for making this available as it has been quite helpful.

    I noticed from comments that many poeple are haveing a hard time making the transition from the old (which was available to me back on 02-23-16) to the new calculator (which I found as the only option today). I, too am having difficulty with the learning curve. I learned from comments that one can use the backspace and then just type in dates. When I do this, the new calculator does not change the number of days automatically, which means one must also calculate this and enter it manually. I am assuming this is not what you intended as it means one must calculate outside the calculator so the calculator can calculate … (at least this is my experience …) Additionally, the locked calculated cells are too greyed out in my printed version (which will likely always be different for different users …).

    This makes your new version much less user friendly than the previous version which was (apparently bug free). While I do understand your need to update so as to make this work on multiple platforms for a wide variety of users, making the older ( tried, true, tested and bug free) version available is something I do hope that you consider.

    Again, thanks for making this available.

    • Mike, thanks for the nice words and the details. Much appreciated.

      It’s not really practical to offer an “old” and a “new” version of each calculator. Too much maintenance. It’s better to make the necessary tweaks to the new design to get them to work the way most people want to see them work.

      That’s one reason for adding a comment section to each page.

      I think you’ll now see the issue you pointed out with the calculated results being grayed out and not printing dark enough fixed. Please try and let me know. (If they still print too light, then press CTRL-F5 to refresh the page so that your browser picks up the latest code.)

      About the dates, I didn’t really say to use the backspace. I think the easiest way to work if you are going type in the dates is to [TAB] from input to input. This leaves the value selected and you should be able to just start typing. The old value will be cleared.

      About the days recalculating. They will recalculate. I’m 100% sure of that. The “secret” however is to tab off the date once it is entered. That tells the calculator to calculate. (You could also click off the date too.)

      Basically, the calculators are designed so a user shouldn’t need to take their hands off the keyboard too often.

    • Gary, an update was released on Monday that seems to have resolved all the issues that were reported with the compound interest calculator including those around entering dates and the default dates I had selected. If you still see any problems, just let me know and they’ll be fixed. It’s not my intention to make this calculator or any of them less useful.

  • I agree, the end date should default to today. If someone is calculating into the future, I doubt it will be one year from today’s date for most people. For my job I work from the past to today’s date.

    Also, I use this daily for my job and it has become highly inconvenient to me and I will likely need to find an alternate calculator. The things that are causing me issues:

    *I cannot use the 10 key to enter date ranges
    *Your system is sensitive and throws a fit when I enter the / myself. It should just enter it if I do, and enter it if I don’t. It shouldn’t stop me in what I am doing to click out of an alert.
    *The end date range being defaulted a year.

    I recognize these are specific to my needs, so I understand how they may not be important to change. The last one is not that important to me, as long as I can use the 10 key, but I cant. The first two issues are just annoying enough to me that I will be looking for an alternate calculator.

    Thank you for allowing access to this tool. That does not go unrecognized.

    • Not being able to use the numeric keypad was certainly a bug. It is now fixed. You happened to be the second person on Friday to have noticed this. I tested on many devices. Notebook. Desktop. Cellphones. I just never tried that numeric keypad. Never got use to using it.

      Allowing the user to type the date separators is another matter. That’s by design and consistent with how the number entry works for amounts. User does not type thousand separators either. I have no objection from a design point of view to allowing the user to enter them – but it’s tricky programming and not high on the priority list.

      The end date now defaults to today.

      So, 2 out of 3. Hope it helps.

      • Karl, I think you nailed it. This now seems like the best online calculator, very convenient and easy to use now that you’ve made the necessary updates. Thanks for listening to your users

      • I would say you got 3 out of 3. As long as I can use the 10 key, I don’t ever feel the need to enter the / myself so that is not even an issue now! So thank you for making the changes, it makes my life so much easier! I appreciate your willingness to hear our concerns and providing an amazing tool to help me with my job. You’re the best!

  • Oh my god, I’ve been using this forever since it was an easy way to calculate interests between dates, but it was so annoying with the comma/period and mm/dd/yyyy format.

    I’m glad it’s fixed now or at least it can be changed.

    Thank you!

    • Wow, you’re right. That was not intentional to drop the 360 day / 365 day year feature. I’ll have to research how that happened and get it restored. But no worries, though the calculator is called “compound”, there is a “simple interest” option under the compounding choice. Please try the compound interest calculator. It does have the days in year option.

  • I love it and use it alot. I agree the end date should default to today. My eyesight must be bad because I confuse the 8’s with the 0’s. But love it. ty

    • Happy you like the simple interest calculator. You should find that the end date defaults to the current date when the page is first loaded. I now see that if a user clicks the “Clear” button that the end date does not default to “today”. I’ll probably get that fixed sometime next week.

      Note that if you click on the plus sign below the calculator, that will increase the size. Perhaps that will make the 8’s easier to distinguish from the 0’s.




    • You’re right. That is really a bug and not an intentional design decision. I’m out of the office the balance of this week. I’ll probably be able to fix that some time early to mid next week. Thanks for taking the time to point it out.

    • Took longer than I thought after a week of R&R, but clicking “Clear” and the end date reverting to the next year has been fixed.

    • Sorry, but the calculator does not support (at this time) a 366 day year.

      There have been two or three requests for this so far. In principle, I don’t have a problem adding the feature, but (1) I’ve never seen a document from a commercial entity that indicates a 366 day year is used. And (2) i’m not sure how it would work if a user spans a time frame that is not within a leap year.

      If you or anyone else has specifications from a reliable source as to how this calculation should be handled, I’m very happy to review them and to try to incorporate the feature into the calculators.

  • Norman Rabek says:

    Thanks a lot for a great, simple calculator. It seemed very intuitive and changing the date was a breeze – just click the date and start entering the new one. Was initially thrown off by the “Days” line, but then saw that it recalculated as soon as I entered a new date. The only suggestions that I would have at this point are to have the start and end date lines as empty boxes with mm/dd/yyyy so that people understood more readily that they could just enter what they wanted, and to have the option of printing a weekly/monthly/yearly summary of the balance and interest accrued. This would be helpful for income tax and other needs. Also, if you really wanted to make it even more versatile, the ability to change the interest rate part way through the term, or sequentially would be a great addition. Thanks again for a great, free, easy interest calculator.

    • Thank you for your comments. I’m not sure about the suggestion about changing how the dates are handled at this point. A few folks have actually asked to have the end date default to the current date.

      As to your suggestion about the schedule, it is a good one. And there is already a calculator on this site that will do just that! 🙂 Please see the Future Value Schedule.

      To replicate this calculator, enter a starting amount and $0 for the periodic amount. Select Exact / Simple for compounding. Click the print preview button. This will give you a schedule showing the accrued interest at the end of each period.

      If you have any questions after trying the calculator, you may leave them at the bottom of that calculator page.

  • Hi Karl,

    This is very helpful tool (thanks for sharing). This calculator shows the interest amount if we input the interest rate. Will it be possible to show the interest rate if we input the interest amount because in most of the cases our account gets credit with the interest amount so it is very difficult to find the interest rates ?


    • You’re welcome Dinesh.

      Good question. No, this calculator won’t do that (I’ll have to think about adding that ability). But there is a calculator on this site that will easily do it. It’s the most flexible / sophisticated calculator I think you’ll find online:

      Ultimate Financial Calculator

      If you scroll down the page there are a number of tutorials. There isn’t one that deals exactly with your question, but there is one that is close. See #22:

      Calculate Rate of Return (ROR) on Annuity

      The difference is, in your case, you are not interested in an annuity, so you’ll have only 1 final series period, not multiple. If you look at it and have any questions, feel free to ask on that calculator’s page.

    • The interest is always calculated for the exact number of days. What is different is how the daily interest rate is calculated i.e. whether the annual interest rate is divided by 360 or 365. Today, taking just the defaults that the calculator loads with Oct. 5, 2015 through Oct. 5, 2016 the calculated interest is 1016.67 for 360 a day year and 1002.74 for a 365 day year.

      Are you getting something different?

  • Hey, I like it. It did exactly what I wanted, as I needed it to. if I was dreaming? The only improvement I might ask for is better page formatting for print or a “Compounded X”.

    But – frankly, I would be very happy with this calculator if it never changed again.

Comments, suggestions & questions welcomed...