Question 1

How do I work out a date a set number of days from now?

Accepted Answer

Pick the start date, type the number of days, and choose add or subtract. The calculator moves across month ends and leap years for you, which is where hand-counting usually goes wrong — 31 January plus 30 days is 2 March in a normal year and 1 March in a leap year.

Question 2

Does day one count as the start date or the day after?

Accepted Answer

This is the mistake that costs people deadlines. Here, adding 30 days to 1 January gives 31 January — the start date is day zero, and the count begins the following day. Contracts and court rules often say the opposite, counting the start date as day one. If a document specifies a method, follow the document; if it does not, most jurisdictions default to excluding the first day and including the last.

Question 3

What is the difference between calendar days and business days?

Accepted Answer

Calendar days count everything. Business days skip Saturdays and Sundays, and usually public holidays too. A '30-day' notice period is almost always calendar days, while a '10-day' processing time from a bank or government office is almost always business days — and the two can be three weeks apart. This calculator counts calendar days.

Question 4

How do I count backwards to find a deadline?

Accepted Answer

Choose subtract and enter the number of days. This is how you find the last date to give notice: take the date the notice has to land, subtract the notice period, and you have the day it must go out. Give yourself a margin if it is going by post.

Question 5

Does it handle leap years?

Accepted Answer

Yes. February gets its 29th day in leap years automatically, so a span that crosses one lands a day later than the same span in an ordinary year. Century years are handled correctly too: 1900 was not a leap year, 2000 was, and 2100 will not be.

Question 6

What are the usual reasons people need this?

Accepted Answer

Notice periods on a lease or an employment contract, return and refund windows, warranty expiry, visa validity, probation end dates, project milestones counted from a kick-off, and prescription refill dates. In each case the answer needs to be a date, not an approximation.

Question 7

How many days are in a month for this calculation?

Accepted Answer

The real number. The calculator moves through the actual calendar rather than assuming 30-day months, so adding 90 days to 1 January gives 1 April in a normal year, while adding three months would also give 1 April — the two agree here and often do not. If a contract says months, count months; if it says days, count days.

Question 8

Can I find the date a specific number of weeks away?

Accepted Answer

Multiply by seven and enter that. Twelve weeks is 84 days, and because it is a whole number of weeks the answer always falls on the same weekday as the start date — useful for anything scheduled fortnightly or monthly-by-weeks.

Question 9

Why does the weekday matter in the result?

Accepted Answer

Because a deadline that lands on a weekend or a public holiday usually rolls to the next working day, and in a few contexts back to the previous one. The result shows the weekday so you can spot that immediately rather than after the fact.

Question 10

Is anything I enter saved?

Accepted Answer

No. The date arithmetic happens in your browser and nothing leaves it.

Span	Calendar days	Roughly, in business days
One week	7	5
Two weeks	14	10
One month	30	21-22
Three months	90	64-65

Add Days to Date

Add or Subtract Days

Result Date

About This Date Calculator

The Off-by-One Problem

Calendar Days vs Business Days

Examples

Frequently Asked Questions

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