Time Calculator

Version 3.5.0

Help | Keyboard Shortcuts | Settings | About Time Calculator



Basic Usage


Multiplication and Division




Version History

About Time Calculator

Doing math with times isn't as simple as doing math with regular numbers because times use a different base. Time Calculator simplifies this problem. It provides:

  • An intuitive, calculator-like interface
  • Support for multiple calculations
  • Limited support for multiplication and division (WARNING: Read the multiplication and division section of help before using those functions—or risk incorrect results.)
  • Memory functions

If you have any comments or questions, feel free to e-mail me.

Scott Severance

Time Format

The format for displaying times is hours:minutes:seconds (e.g., 2 hours, 30 minutes, and 15.4 seconds is displayed as 2:30:15.4). When entering times, the selection box (outlined in red) determines whether you are entering hours, minutes, or seconds.

Click : to advance the selection box. Alternatively, you can click directly on the calculator screen to set the selection box.

IMPORTANT NOTE: Time Calculator supports hours, minutes, and seconds. It doesn't yet know anything about days. Thus, hours outside the range 0-23 are acceptable. If you need to handle days, you can do a manual conversion. For example, 14:00:00 - 15:00:00 = -1:00:00. If you add 24 hours (-1:00:00 + 24:00:00), you'll get the time on the previous day (23:00:00). Remember that this is just a workaround, as Time Calculator has no idea about days. Support for days is on my list of features to add, but I don't have a whole lot of spare time these days.


Most buttons work as expected. Here are some special buttons:

  • : Advances the selection box.
  • . Inserts a decimal point. This button is disabled if the selection box is not on the seconds field.
  • Backspace key. Deletes the last number from the selected field.
  • AC Clears the the screen and resets the calculator. However, AC doesn't clear the memory.
  • C If the value on the screen is not 0:00:00, resets the screen without resetting the calculation. Otherwise, behaves like AC.
  • M+ and M− Add/subtract the value displayed on the screen to the value currently in memory; or, if memory is empty, sets memory.
  • MR Displays the value stored in memory on the screen, replacing whatever is currently on the screen.
  • MC Clears the memory.

Unless you want to multiply or divide a time by another time (you probably don't), be sure to enter the non-time factor in the seconds field. If you don't, you will get unexpected results. As a reminder, the selection box is moved to the seconds field whenever you click × or ÷.

Here's why: Before calculating, all values are converted to seconds. That means that 0:30:00 × 0:00:2 gets converted (in part) to 0:30:00 × 2 and will output 1:00:00 as expected. However, 0:30:00 × 0:2:00 gets converted (in part) to 0:30:00 × 60 and will output 60:00:00. 0:30:00 × 2:00:00 gets converted (in part) to 0:30:00 × 7200 and will output 3600:00:00.

Keyboard Shortcuts

To enter a number, type it. For other keys, refer to the table below (note that many buttons can be activated by several keys):

ButtonKeys      ButtonKeys
++ P - M
×* T ÷/ D
== Enter E .. , V
B < Backspace :: Tab Right Arrow Space S
CC Delete Clear ACA Esc
HelpH ? Keybd.

How can I enter 2 PM?

The calculator works with absolute times, so it is unaware of the time of day. You can't enter PM, just as you can't enter AM. Just enter the raw hours, minutes, and seconds.

If you're trying to find out how long you worked if you started at 8:22 AM and quit at 5:35 PM, you can convert to 24-hour time by adding 12 hours to every PM time. So, you can enter

5:35:00 + 12:00:00  8:22:00
to get the total time you worked, 9 hours and 13 minutes.

Is there an iPhone or Android app?

An Android app is planned, but not ready yet. An iPhone version is unlikely since I refuse to buy Apple products and thus have no way of testing such an app.

  • Some keyboard shortcuts don't work in all browsers. All such keys have alternatives. If the one you tried doesn't work, try one of the alternatives.
  • The Button doesn't work in older versions of Internet Explorer if the selected field contains more than one digit.
Key mapping

Users of the numeric keypad might prefer that the key . activated : instead of .. Here's an option you can set:

On some systems, using the Alt+Tab keyboard shortcut to switch between windows also causes the selection on the time calculator to advance. This option prevents this. Note, however, that it also disables the tab key to advance between fields.

Output format

Some users may prefer times to be always displayed in minutes and seconds, instead of hours, minutes, and seconds.

Time Calculator 3.5.0

March 11, 2024

  • Converted the source code to TypeScript and switched the math library from BigDecimal to Big.js. This required some modernizing of the code, as well.

Time Calculator 3.4.2

November 22, 2020

  • Because on some systems hitting the Alt+Tab keyboard shortcut to switch windows causes the selection to advance, added an option to disable that functionality of the tab key. As a consequence, when the option is enabled, the tab key won't perform its normal function, either.

Time Calculator 3.4.1

April 18, 2018

  • Slightly modernized the calculator’s appearance
  • Fixed display issues apparently caused by changes in browsers over the years

Time Calculator 3.4

August 15, 2015

  • Added an option to display times in minutes and seconds instead of hours, minutes, and seconds. Thanks to Patrícia Bateira for the suggestion.
  • Added close button to help.
  • Certain versions of Chrome caused a problem by navigating back instead of deleting a number when the backspace key was pressed. Fixed.

Time Calculator 3.3.1

July 24, 2012

  • Fixed a bug in the memory feature that was introduced by the change to BigDecimal in version 3.3.
  • Fixed the stripTrailingZeroes functionality.

Time Calculator 3.3

December 30, 2011

  • Fractional seconds are now calculated correctly. This has been a longstanding bug, and I'm happy to have it fixed thanks to the awesome BigDecimal.js.

Time Calculator 3.2.1

September 12, 2011

  • Fixed two Internet Explorer bugs:
    • When there is another window open, the IE window with the time calculator no longer jumps behind all other windows.
    • The operators are no longer cut off from the edge of the tape in IE.

Time Calculator 3.2

September 11, 2011

  • Hopefully fixed a bug that caused Internet Explorer windows to jump behind all other windows in some cases.
  • Fixed several bugs related to the history tape. The tape should now be easier to understand.
  • Enhanced the documentation by adding a FAQ section and updating the bugs section to remove obsolete bugs and to reflect the problems with floating point math.

Time Calculator 3.1

November 12, 2010

  • Users can now click entries on the history tape to copy the value to the calculator screen. Thanks to Kevin Matzdorf for suggesting this.
  • Fixed a long-standing bug related to multiple calculations. Now, clicking operation buttons after a result is displayed, or clicking different operation buttons in succession works correctly.
  • Better error handling
  • Minor fixes/enhancements

Time Calculator 3.0.4

November 3, 2010

  • The calculator now remembers the value of the ". as :" keyboard setting.

Time Calculator 3.0.3

October 28, 2010

  • Added note to the "Basic Usage" section of the help explaining Time Calculator's lack of support for days. Also suggested a workaround.
  • Fixed some typos.

Time Calculator 3.0.2

August 12, 2010

  • Fixed a bug that kept Time Calculator 3 from working in older versions of Internet Explorer.
  • Minor UI changes.

Time Calculator 3.0.1

August 8, 2010

  • Changes made to 3.0 broke older versions of Internet Explorer. Since I don't have access to any version other than 8, I'm not able to find and fix the problem. This version presents users of older versions with several workarounds.

Time Calculator 3.0

August 1, 2010

  • Time Calculator now has a memory.
  • Added a calculation history panel.
  • Vastly improved keyboard handling. Using the calculator via the keyboard should now be much simpler. See the keyboard help section for details.
  • Added an option, located under keyboard shortcuts, to map the . key to the : button in order to simplify entering times via the numeric keypad. This option is disabled by default. Thanks to Todd Andrews for the suggestion.
  • Several user interface enhancements.
  • Significant code cleanup.

Time Calculator 2.4

October 28, 2008

  • Replaced the algorithm to convert from seconds to hours, minutes, and seconds. The old algorithm was really inefficient, especially for large values.

Time Calculator 2.3

May 4, 2008

  • Added keyboard shortcuts

Time Calculator 2.2

February 28, 2008

  • Clarified the legal language as regards distribution
  • Dropped the 2 from Time Calculator, and dropped the link to Time Calculator 1

Time Calculator 2.1

January 9, 2006

  • Minor user interface enhancements
  • Added legal language to the about page
  • Added version history page

Time Calculator 2.0

January 8, 2006

  • Completely new interface
  • Completely new back end
  • Added limited support for multiplication and division
  • Added support for multiple calculations

Time Calculator 1.0


  • Initial release
  • Addition and subtraction
  • Single calculations only

Time Calculator 3.5.0
Copyright © 2001-2024 by Scott Severance
All rights reserved.

NOTE: The following terms apply to the Internet edition of Time Calculator (which you are currently using). Separate terms apply to the download edition.

You may freely use Time Calculator, but if you want to copy it, mirror it, distribute it, modify it, or create a derivitive work, you need my permission.

The intent of these terms is to ensure that Time Calculator is only available on one website. You may, of course, link to Time Calculator. You don't need permission to do so. Restrictions on how you may link (as some sites use) are bogus. However, I request that you don't frame my site.

Time Calculator has no warranty of any kind whatsoever (not even an implied warranty). Use it at your own risk. If your jurisdiction does not permit such warranty exclusions, you may not use Time Calculator.

If you have any questions or suggestions, drop me a line. Many of the features of Time Calculator are the direct result of user feedback.

Copyright Notices

The following notice applies only to the BigDecimal.js library used by this calculator:

To enter numbers, just start typing. To change fields, press Space or :.

Calculation History
(Click entry to
copy to calculator)