plus date math calculator

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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.

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.

Loan Carrying Cost: Interest Reduction Techniques

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.

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! :)

Why oh why did you change the layout and the print parameters? Only two weeks ago I could print a calculation that had print large enough to read and when I pressed Print, all I got was my calculation. Now it starts printing at the bottom right corner of a page going to a second page with the rest of the calculation at the top right corner and then a third wasted page because it is blank.

As well, interest earnings on my original prints were within 9c of the final figures provided by my bank, and now they are way off – to the tune of like $70 too high!! I’m very disappointed as I thought I’d finally found an accurate and easy to use calculator.

I’ll take each one of your points individually.

>>>Why oh why did you change the layout and the print parameters?

Primarily there were 2 reasons.

1. This new layout works much, much better on a wider variety of screen sizes. The calculators are designed to now work on mobile and tablets as well as desktop computers.

2. I wanted to incorporate a comment area so users can leave feedback. I fully expect changes to be made to the calculator and to the site in general as I learn more about what users need and want.

>>>Now it starts printing at the bottom right corner of a page going

Printing can definitely be improved (and will be as time goes on). But what browser are you using? I”ve tested with Google Chrome and Microsoft’s IE 11. Chrome is definitely the better option. IE should work. If you are using the new “Edge” browser from Microsoft, it seems to have a bug and it ignores the styles setup for printing.

That said, about the size, if you increase the size of the calculator, that also increases the size of the print out. (Click on the “+” under a calculator).

>>> – to the tune of like $70 too high!!

This, of course is the most troublesome comment. The calculations, I don’t believe, change between the old and the new version of this calculator.

However, some of the setting did change. We had requests from users that the days in year setting change to 365 has the default. It had been 360 on the older calculator. This will certainly lead to different result.

That’s not to say there was not an error made in setting up this calculator.

If you can give me a specific example, I would like to look into this more. And naturally, any bugs in calculations will be corrected.

Thanks for taking the time to comment.

The new calculator gave me a different result than the old calculator. See below.

Old Calculator

$52,200 loan amount at 6.00% Loan Date 6/16/16 Closing Date 1/29/16 Interest amount calculated was $1974.90.

New Calculator-calculated interest amount of $1947.85

Which calculation is correct?

First, I assume that the closing date is 1/29/2017 and not 2016.

They are both right!

The compound interest calculator and all the calculator on this site support a lot of options that impact the results. Normally we suggest leaving the setting set to their defaults – that is, to the way they are set when the page first load, unless you have a specific reason to change them.

And that’s what you did. However, this calculator’s “Days In Year” default value changed from the last version due to comments by users that they felt 365 is a more appropriate value.

If you set the calculator to 360 days in year, you’ll get the result you had gotten previously.

Both are correct, if you account for the fact that the bank will steal your money by calling it fees! fee for opening the account, fee for administrative management of your money, fee for uncle Sam’s tax (just because you are saving your own money that you already paid taxes on), fee for withdrawal, fee for deposit, fee for not doing anything with the account at all, fee for getting your money out at an ATM, fee for just being your crooked friendly neighborhood bank location, fee for…. did I mention lack of activity in your account? Yep, they charge you for not doing anything at all with the money in the bank.

Hi,

Just wondering if you could make the older version of the calculator available to use again. I have to calculate interest using older years – 2000 to now. it was much easier on the older calculator to scroll to the exact date and year that I needed.

Or on this version if you could somehow make the calendar move month to month and add another button so it moves year to year?

Btw, thank you so much for offering this calculator online for free. It is one of the best and most useful calculators to use for calculating interest using specific dates and has made my work so much easier over the years.

First, thank you for your kind words. I’m glad you have found the calculator useful.

About the dates – I understand. However, I think it’s more a matter of not having enough documentation or making the calendar use more intuitive.

Please note: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:

03042016.2. 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 (making sure you explicitly click on all 3).

3. If you need “today’s date” click on the word “Today” at the bottom of the calendar.

Hopefully this helps.

I hate this new format and it will not work on my computer. Time to go

elsewhere.

Dot, thank you for your follow-up email. About the printing. I think you’ll find it to be much better. If at first you don’t, it might be because your browser still has old programming code loaded. Please press CTRL-F5. This will cause your browser, when on this page, to load the latest version of the calculator.

I still need to get rid of that stupid message that users see about there not being anything to calculate. Hopefully, that will happen sometime next week.

If you find any other problems, please let me know. I do want to fix them.

I just wanted to briefly say that I have used your site and/or calculator for a few years now. I actually have this website saved on my browser as one of my “Favorites”. The recent changes are nice. I’m still getting use to them because I haven’t had a need to try everything yet. But in general, thanks so much for what you’ve made available to us. Personally, it has helped me immensely.

Thank you. I appreciate the comment. The site still has some kinks. If you find any, let me know and we’ll review them and make the necessary changes.

If you use a smart phone or tablet, the site will work much better now on those devices. That is the major reason for all the changes.

Hello Karl – thanks for the calculator. I’m learning finance at school and learnt about FV function in excel. I tried replicating a calculation in excel for a 390 day CD with quarterly compounding. The maturity value I get using your calculator matches what I see from the bank – that is good 🙂

But the FV using excel is correct only if the # of days was a multiple of 365. Seems like if there is a fraction in the # of periods, the calculation in excel is off. I’d appreciate if you give some insights on what is wrong. Here is the example.

PV: 1,37,478

Annual rate: 9%

Days: 390

Days/yr: 365

Quarterly compounding

FV: 1,51,201.00 (This is FV the bank is paying me)

My excel function:

FV( (0.09/4), (4*390/365), 0, -137478, 0)

It appears if nper (second argument) is not a whole #, my calculation is off.

Hi Vinod, you’re welcome.

It’s not clear to me what you are asking, but in general, I’m not really able to answer questions about Excel here. I would say however, that Excel’s FV formula does not work with whole periods and exact fractional days like this calculator. Rather it works with whole periods and fractional periods.

That’s not necessarily wrong, it’s just a different way to calculate future value and interest.

This calculator calculates interest for the number of whole compounding periods between the two days and then interest for the number of days remaining. It uses the US Fed’s method of counting backwards from the last date to the front date.

Thank you for producing this calculator. It is a great tool, as a person who normally uses a HP12C I find your calculator a great find. Thank you again, Tony.

Hi Karl, these is an excellent and useful calculator, thanks for your job and time. Efrain.

hi karl

we want to download this format calculator on my apple mobile offline version.

so plz send me the link.

thanks with regards

amit garg

Hi, I’m sorry, but we don’t have a version that runs locally on any Apple devices.

I received a calculation from the escrow company and they had put in the amounts, dates etc. from your calculator on your web-site for April 13, 2016. I have tried putting in the same calculations and am getting different numbers. I don’t know what I am doing wrong but would like to add the ending date as of 4/26/2016 and the amount comes out less than the previous end date of 4/13/2016. Please help.

Amount: 2,036.04 at 12.0000 interest from 11/7/2011 to 4/26/2016 is what I am trying to calculate. The interest from 11/7/2011 to 4/13/2016 was $1,447.30 previously and now it is $1420.86. Thank you so much!

I guess the question is why someone got $1,147.30 interest for the period from 11/07/2011 to 04/13/2016? I’ve been playing with this for a while and I can’t see how anyone got that number. Your post is a bit hard to reply to though because you don’t ask an explicit question and you leave out some details such as what compounding frequency you are using and what days per year. But assuming monthly compounding and 360 days per year you should be getting $1,420.86 through 04/13/16 and $1,435.81 through 04/26/16. If I’ve missed something, please let me know.

Really informative forum topic.Really thank you! Schwartzbach

Hi –

Just wanted to let you know how much I appreciate this calculator. Like others this is bookmarked and I have shared it with others. The fact that you make all the parameters visible, including compounding rate makes your calculator unique among all the calculators out on the web.

I scanned through the recent comments and did not see a question regarding leap year. Does your model account for leap year? On a hunch, I pushed out the “End Date” for the number of leap years that would have been encountered over the elapsed duration (in my case 2) , and that led to a value that is within 0.05 of what the system returned.

I was curious if industry has a standard way of addressing leap year in FV calculations.

Thanks

Thank you for your kind words and thank you particularly for telling others about this site.

About leap years, all calculators on this site do account for them. However, spanning a leap year will not always impact a calculation. The impact depends on the compounding selected. "Continuous", "Daily" and "Exact / Simple" compounding are day based frequencies and therefore, a February 29th will increase the interest accrued for any period that it is included in. If you select a month based or week based compounding frequency, then spanning a leap year will have no impact.

But then that is no different than calculating interest for March or April. If you use the calculator’s defaults and change the compounding to "Monthly" and check Mar. 1 to Apr. 1 and then Apr 1 to May 1, (full months, but different number of days of course) the interest will be the same.

If this doesn’t answer your question, please follow-up with another.

Is there an amortization schedule for this calculator?

There are several calculators on this site which can create amortization schedules and various other cash flow schedule too. Here’s the one that you probably want: Amortization Schedule and Calculator.

Let me know if there’s some particular feature you need that you don’t see.

Hi

Can we expect a mobile app for the same? I am ready to pay for it. Your site has the most comprehensive calculators I have seen with lots of options.

Hello, presently, I have no plans for native mobile versions. There is quite a bit more that I want to add to the website. However, I’m very interested in why you ask? The calculators, with few exceptions, should work just as well with a mobile browser as with a desktop browser. With the compound interest calculator specifically, I don’t know how it would look or work any differently if it were a native app versus this one that is on this page.

Am I missing something?

I have a few suggestions regarding this calculator’s input:

1. Users should be allowed to use ALL keys with their functions unaltered. Nothing is more frustrating than trying to change “1500” to “1300” without having to re-enter the whole value and constantly closing the alert popup when trying to change just one number within the value.

2. Single-clicking a value shouldn’t select the everything (because that’s what double-clicking is for). I generally click on text to move the input cursor to a specific location if I’m not using the arrow keys/home/end to navigate.

3. Users should not be warned about trying to type slashes in the date input box. There are better solutions. It is frustrating to hit a key out of habit and have to close the alert before continuing.

4. Users should be able to hit enter in any of the input boxes to perform a calculation without clicking on Calc.

Suggestion 4 goes with suggestion 1; it would have allowed me to quickly test several starting amounts for the same time period instead of being forced to deal with the clunky input system and clicking the button over and over again.

This calculator is very frustrating to use with how it mangles my input.

Thank you for taking your time to write up your thoughts.

I guess depends on the user’s mindset when they use the calculator. This calculator’s inputs are designed to work the way a digital calculator’s work. The numbers are right aligned and each digit moves to the left as the user types numbers with the thousand separators automatically being entered. The user does not type anything but numbers (for dates as well). The numbers are intentionally selected when a user clicks on them or tabs to them so they can immediately start typing. The prior value is cleared as soon as the user types one digit. No need to backspace or delete.

In my opinion, the very best way to use the calculator is to use the tab key (or shift-tab to go in reverse) when moving from input to input. Tab to a field and start typing number. Frankly, it will be much faster and easier to just type four digits for “1300” rather than to try to click to the right of the 5 and hit backspace and retype 3. By tabbing to the 1500 of clicking on it, the value is select so that a user doesn’t have to bother to try to edit a single digit. It’s too tedious and time consuming.

If you DO want to edit a number, hit the right arrow key. This removes the selection. Then, like a calculator, backspace to the digit you want to change, retype it and then reenter the remaining digits.

>>>> I generally click on text to move the input cursor to a specific location

Basically, a user shouldn’t have to do this. While moving the cursor, they could be typing the digits.

I wish you had left a real email address. But you don’t seem to be open to the idea that there may be valid reasons why the calculator is designed the way it is designed.