Date Add & Subtract
Adds or subtracts days, weeks, months or years from a date, optionally skipping weekends and holidays.
A date plus or minus a span: so many days, weeks, months or years out from a starting date. Skipping weekends and holidays turns it into the deadline calculator, which is what most people want it for.
Result
2027-02-18
Day
Thursday
Months are added by clamping the day: 31 January plus one month is 28 February, the same answer every calendar app gives.
How to use it
Set the starting date
Today by default. This is day zero, not day one — adding one day to the 1st gives the 2nd.
Type the amount and the unit
Negative numbers go backwards, so there is no separate subtract mode to look for.
Skip non-working days if it is a deadline
With that on, adding ten days from a Friday lands on the Friday after next rather than on a Monday two weeks out.
Common questions
What happens to 31 January plus one month?
It gives 28 February, or 29 in a leap year — the last valid day of the target month. There is no 31 February, and the alternative convention of rolling into March surprises people more often than it helps.
Does adding months then subtracting them get me back?
Not always, and that is arithmetic rather than a bug. 31 January plus one month is 28 February, and 28 February minus one month is 28 January. Month arithmetic is not reversible at the ends of months.
Which holidays are excluded?
Korean public holidays, including the substitute days that fall when a holiday lands on a weekend. Lunar dates such as 설날 and 추석 are computed from the lunar calendar rather than looked up in a fixed table.
Feed it from
Date Difference
Counts days, weeks, months and years between two dates, with a D-day view and business-day option.
Business Day Counter
Counts working days between dates, or finds the date N working days out, excluding weekends and holidays.
Add-to-Calendar & ICS
Builds Google, Outlook.com, Office 365 and Yahoo calendar links plus a downloadable .ics that Apple Calendar and Outlook desktop read.
Unit Converter
Converts length, weight, area, volume, temperature, speed, pressure and data units, including Korean units.
Next
These accept what this tool produces, so the result can go straight in.
Business Day Counter
Counts working days between dates, or finds the date N working days out, excluding weekends and holidays.
Add-to-Calendar & ICS
Builds Google, Outlook.com, Office 365 and Yahoo calendar links plus a downloadable .ics that Apple Calendar and Outlook desktop read.
Date Difference
Counts days, weeks, months and years between two dates, with a D-day view and business-day option.
Korean Public Holidays
Lists public holidays and substitute holidays for a year, including the lunar-dated ones, as a calendar or ICS.
CSV Viewer
Opens a large delimited file with type detection, column stats and sorting, without loading it all into memory.
Currency Converter
Converts between about thirty currencies at the ECB’s daily reference rates, crossed through the euro, or at a rate you type in.