Tool to make calculation with dates. Date can be computed with additions or subtractions of days, weeks, months or years with a given date.
Calculation with Dates - dCode
Tag(s) : Date and Time
dCode is free and its tools are a valuable help in games, maths, geocaching, puzzles and problems to solve every day!
A suggestion ? a feedback ? a bug ? an idea ? Write to dCode!
Calculation with Dates
Addition of days to a given date calculator
Subtraction of days to a given date calculator
Number of days since a date
Answers to Questions (FAQ)
What is the addition of days to a date? (Definition)
The calculation of addition or subtraction of a number of days N to a given date makes it possible to define another date, in the future (or the past) located at an interval of N days.
It is very used for countdowns before an event, or to calculate an age in number of days.
Example: 135 days before the next Olympic Games
How to add/remove days to a date?
dCode locate the day, month and year in a reference calendar and add or subtract the number of days required for the initial date to calculate the new date.
Example: To determine when somebody had/will have 10,000 days, add 10000 days to the date of birth.
Calculation uses the Gregorian Calendar and the Julian one before 1582.
It is possible to get good approximations using the values: 1 week = 7 days, 1 month = 30.4 days (average value), 1 trimester = 91.3 days (average value), 1 year = 365.24 days (average value)
How to calculate your age in days?
To know how many days somebody has, use the difference between two dates tool and enter the birth date and today as the reference date for subtraction.
How to add days of months in Excel
To add days in Excel, add an integer to a date.
Example: 2010/01/01 + 1 = 2010/01/02
To add months, use the function EDATE
Example: EDATE("01/01/2010",1) = 2010/02/01
Source code
dCode retains ownership of the "Calculation with Dates" source code. Any algorithm for the "Calculation with Dates" algorithm, applet or snippet or script (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, breaker, translator), or any "Calculation with Dates" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) or any database download or API access for "Calculation with Dates" or any other element are not public (except explicit open source licence). Same with the download for offline use on PC, mobile, tablet, iPhone or Android app.
Reminder: dCode is an educational and teaching resource, accessible online for free and for everyone.
Cite dCode
The content of the page "Calculation with Dates" and its results may be freely copied and reused, including for commercial purposes, provided that dCode.fr is cited as the source (Creative Commons CC-BY free distribution license).
Exporting the results is free and can be done simply by clicking on the export icons ⤓ (.csv or .txt format) or ⧉ (copy and paste).
To cite dCode.fr on another website, use the link:
In a scientific article or book, the recommended bibliographic citation is: Calculation with Dates on dCode.fr [online website], retrieved on 2025-07-19,
