Add Days Calculator

What the add days calculator does

This is the most direct date tool there is. You have a date, you want the one that is a set number of days later, and that is the whole job. Pick a date, type how many days to add, and it gives you the new calendar date, plus the day of the week it lands on. The date box starts on today, so for "what is the date 30 days from now" you only need to type the number.

It handles the awkward part for you, the way a run of days crosses the end of a month or the turn of a year, so you never have to count past the 31st in your head.

How to use it

1. Select A Date. The date you are counting from. It starts on today, so change it only if you need a different start.
2. Days to Add. How many days forward. To go backward instead, enter a negative number.

Press Calculate and the new date and weekday appear.

How the new date is worked out

Under the hood it uses Moment.js, a well-known date library, to do the work. It hands your date and your number of days to Moment, which adds them and rolls the result across month and year boundaries correctly, then it asks Moment for the weekday of that new date. Adding the days is the easy half. Getting the month lengths and leap years right as the count spills over is the part the library quietly takes care of, which is why a date 45 days out comes back correct without any fuss about how many days February had.

An example with real numbers

Say you start on 10 January 2025 and add 45 days.

• There are 21 days left in January after the 10th, which takes you to the 31st.
• The remaining 24 days carry into February, landing on 24 February 2025.

So 45 days from 10 January 2025 is 24 February 2025, and the tool also tells you which weekday that is. You did not have to think about January having 31 days, the count just flowed across the month.

The weekday, which is often the real answer

It is easy to overlook, but the weekday the tool gives you is frequently the thing you actually wanted. When you work out a date that is a number of days away, the next question is usually what day of the week it is. Does that 30-day deadline land on a weekend? Will a delivery window close on a Sunday? Rather than finding the date and then checking a calendar to see what day it is, this gives you both in one go.

Where you would reach for it

Any plain "this many days from now" question. A 30-day payment window from an invoice date. A returns deadline a set number of days after a purchase. A shipping or delivery estimate. A simple countdown target. Because you can also enter a negative number, it doubles as a way to step back, to find the date a certain number of days before something.

Questions people ask

Can I subtract days as well as add them?

Yes. Enter a negative number of days and it counts backward, giving you the date that many days before your start date.

Does it skip weekends?

No. It counts every calendar day, weekends included. If you need to add working days only and skip Saturdays and Sundays, the business days calculator handles that.

Will it tell me the day of the week?

Yes. Along with the new date, it names the weekday it falls on, which is often the most useful part when you are checking a deadline.

Does it handle the end of the month and leap years?

Yes. As the days run past the end of a month or across a leap-year February, the result rolls over correctly, so the final date is always a real one.

References

1. Moment.js, the JavaScript date library used to add the days and read the weekday. https://momentjs.com/