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Stupid Geek Tricks: How to Perform Date Calculations in Windows Calculator

Would you like to know how many days old are you today? Can you tell what will be the date 78 days from now? How many days are left till Christmas? How many days have passed since your last birthday? All these questions have their answers hidden within Windows! Curious? Keep reading to see how you can answer these questions in an instant using Windows’ built-in utility called ‘Calculator’.

No, no. This isn’t a guide to show you how to perform basic calculations on calculator. This is an application of a unique feature in the Calculator application in Windows, and the feature is called Date Calculation. Most of us don’t really use the Windows’ Calculator that much, and when we do, it’s only for an instant (to do small calculations). However, it is packed with some really interesting features, so lets go ahead and see how Date Calculation works.

To start, open Calculator by pressing the winkey, and type calcul… (it should’ve popped up by now, if not, you can type the rest of the ‘…ator’ as well just to be sure). Open it. And by the way, this date calculation function works in both Windows 7 and 8.

Once it’s open, click View, and select Date Calculation (or press Ctrl+E).

Now here’s where the fun begins.

The idea is pretty straightforward. You can perform two types of calculations here:

  • Calculating the difference between two dates
  • Adding or subtracting a number (days) to a date

Since we are messing with dates, it is easy to work with the past, present, or even future. Let’s say you want to find out your current age in terms of days, months, and years. Click the Calendar button in the From field to select your birth date. Initially, it will be showing the current date. Navigating through the calendar is easy. Click the title (Month), and it zooms back to show all the months of the year and the title is changed from Month to Year (in this case, November to 2012). Click it again to see a list of years in the current decade, and the title changes to the decade it is showing (alternatively, click the buttons on the left and right to move between years). Click the title again to show several decades.

You can use the buttons at the left and right to navigate within months, years, decades, or list of decades. Finally, to jump to the current date, click Today.

Now that you’ve learned how to navigate through the calendar, you can easily select your birth date (let’s assume it’s the 29th of February- Geeky, isn’t it?). Since we’re going to find out how old you are today, so in the To field we’ll use today’s date by clicking ‘Today’.

(Yes, the date denoted in the Today field is the date on which this post was written!)

Finally, click Calculate to get the desired result. The resulting difference will be presented in terms of years, months, and days, and simply in days as well.

Adding or subtracting a number to a specific date is a bit tedious in real life. For instance, you see this written somewhere: “43 days remaining!”, and you ask yourself “What will be the exact date after 43 days have passed”?

I’d probably tackle it this way- Lets see, if today is November 16, and this is a 30-day month, so after 40 days it will be December 26, and adding 3 to it makes 29th December. But what day will it be? Well, maybe we should try a different approach instead. Fire up calculator, click the drop down and select “Add or subtract days to a specified date”.

Now there’s just one date field in which we have to specify the date to (or from) which you want to add (or subtract) a particular number. Once the date is set, select whether we want to add or subtract something. We’ll try addition first. Select Add, and enter the number of days (or months/years) to be added to the specified date, and press the Calculate button.

So it will be Saturday on 29th December, 2012.

You can also specify how many days, months, or even years are to be added or subtracted from the set date.  Once you’ve entered the information, click Calculate and you’ll be presented with the resulting day and date. Let’s see what the date was, 5 years, 8 months and 80 days ago today.

And here’s a fun fact. You won’t be able to use the calculator itself, unless you turn it on by clicking its ‘screen’ (just in case you want to convert days to weeks, or do any other calculation).

What interesting date calculations can you come up with? Let us know in the comments!


Here’s one for you: Windows 8 was released how many days after the release of Windows 1.0? First one to calculate gets a virtual high-five!

Here's our very own regular reader. He's an aspiring tech writer, and obsessed with all things tech!

  • Published 11/24/12

Comments (25)

  1. user

    9720 days

  2. user

    9751 days

  3. fksysko

    Cool. Playing with dates has always been tedious to me at least. This’ll really help. Thanks.

  4. GeekinTexas

    When I was younger, I remember figuring out that I’d be 9999 days old on 8/8/88. Seemed cool. This makes it easy. I couldn’t enter more than a three-digit number into the number of days to add, so it took some trial and error with the difference function to figure out when my 20,000 day birthday will be.

    It seems to me that celebrating birthdays involving number of days of nice base ten numbers makes as much or more sense than celebrating the number of times our planet has gone around the sun. :-)

    I know other people that are only interested in powers of 2. Who cares about 8000 days when 8192 is coming soon!

  5. MMSDave

    And Lupu 528 @ 130 mb has a similar feature in its day planner.

  6. Bob

    25203 days

  7. WhytteDragun

    The only thing that struck me as odd about this article is the fact that the author seems to think that you need to wait until Windows finds the calculator exe and then click on it. It is simpler and faster to just – Start Button C-A-L-C Enter – and you’re done.

  8. srsly tho

    I feel ashamed for never noticing them before.
    Thanks for the tip, HTG.

  9. NSDCars5

    Yay! 55 days to my birthday! :P

  10. thatsawrap

    27993 days

  11. Tomer Mansoor

    Diff between Windows 1 release date and Windows 8 “General” release date: 9837 days
    Diff between Windows 1 release date and Windows 8 “Manufacturing” release date: 9751 days
    :) a very handy tool, thanks !

  12. darkprop

    9670 días

  13. Lynda Sanders

    Thanks for the tip. I too never noticed the date function in the many times I have used the calculator.Good thing us dummies have you.

  14. Jane

    @WhytteDragun- Widows key faster than mouse & Start button every time. Widows key+c+Enter snaps calculator open NOW ! (if not; after pressing Widows key+c check the Start menu and use down arrow then Enter)

  15. Art€

    Yep, great to know; I’ve got the utility on another USB portable programme, but this is handy. Thanks.

  16. indianacarnie

    My Asus Has A Dedicated key for the calculator, just one click and its there! been using it more and more lately……. maybe because 20549….lol

  17. Bernard

    Well! It just goes to show there is always something new to learn.

  18. David Hudson

    Works really well! I put in the question ” I was born 4/27/63 and am heading from Seattle to Spokane in my chevy truck. This time of year the passes get snowed in, and my aunt Louisa, who has a pregnant cousin, wants to bring her dog and xbox along to sing in the choir (I think just her not the dog) and to take some pictures. Well, I don’t mind trying to use a map while I’m drinking coffee, but I need to know if I should buy cantalopes in king county or from my from my barbers cousin who has asthma, or what?” Don’t you know it answered almost right away, after the smoke let up some..?
    I KNEW the answer was “what” Sometimes it helps to be reminded to go with your gut feelings by a professional though.Thanks Bill Gates!

  19. Usman

    ^ Nailed it.

  20. Dan

    OK got your full name and your Date of birth David, now if you would please let me know, just what is your mothers maiden name? ;)

  21. Billy

    9837 days

  22. CoolHappyGuy

    Excellent! No more using Excel for these functions.

  23. LAST

    “To start, open Calculator by pressing the winkey, and type calcul… (it should’ve popped up by now, if not, you can type the rest of the ‘…ator’ as well just to be sure). ”

    –you can just type “calc” HAH!

  24. Taylor Gibb

    You can also use PowerShell: (Get-Date).AddDays(7)

  25. zdiggler

    My keyboard have Button for Calculator :)

    and I’m 13,225 days old.

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