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Date Calculator

A free online date calculator that adds or subtracts a chosen amount of time — days, weeks, months, years, or business days only — from any starting date. Doubles as a due date calculator (start date + duration forward) and a business days calculator (skip weekends), showing exactly what date and day of the week you land on.

How the Date Calculator works

Pick a start date, choose Add or Subtract, enter an amount, and choose a unit — days, weeks, months, or years — or switch to business-day mode to skip weekends automatically. Press Calculate to see the exact resulting date and its day of the week.

Calendar units vs. business days

Calendar mode adds or subtracts a fixed span of time exactly as written on a calendar — 90 days is always 90 days, regardless of weekends. Business-day mode instead counts only Monday through Friday, skipping every Saturday and Sunday, which better reflects deadlines quoted in 'business days' rather than calendar days.

How month and year additions handle short months

Adding months or years uses standard calendar arithmetic. If the resulting month is shorter than the start day (for example, adding one month to January 31st), the date rolls forward into the next month, the same way most calendar and spreadsheet software handles it.

Common Mistakes to Avoid

Assuming 'business days' and 'calendar days' are interchangeable

Solution:

A 10-business-day deadline starting on a Monday lands two weeks later on the calendar, not 10 days later — always check which unit a deadline is actually quoted in.

Forgetting the start date itself doesn't count as day one

Solution:

Adding 1 day to a date moves to the very next calendar date — the start date is the reference point, not the first day counted.

Not accounting for month-length differences

Solution:

Adding 1 month to January 31st doesn't land on 'February 31st' (which doesn't exist) — it rolls into early March, since months have different lengths.

Using calendar mode when a holiday-aware business-day count was needed

Solution:

This calculator's business-day mode skips weekends only — it doesn't exclude public holidays, so deadlines that also skip holidays will land a little earlier than this calculator shows.

Entering a negative amount instead of using the Subtract option

Solution:

Always enter a positive amount and use the Add/Subtract toggle to choose direction — a negative amount isn't accepted.

Confusing weeks with a fixed 7-day multiple of business days

Solution:

A 'week' in calendar mode is always 7 calendar days, not 5 business days — use business-day mode if you mean 5 working days.

Frequently Asked Questions

Set the start date to today, choose Add, enter the number of days, and press Calculate.
Calendar mode counts every day, including weekends. Business-day mode counts only Monday through Friday, skipping Saturdays and Sundays — useful for deadlines quoted in working days.
No — business-day mode only skips weekends. It doesn't exclude public holidays, so a holiday-aware deadline may land a little earlier than shown here.
Yes — use the Subtract option to find a date that many days, weeks, months, or years before your start date.
The date rolls forward — for example, adding one month to January 31 lands in early March, since February doesn't have 31 days.
Yes — choose Weeks as the unit and enter how many weeks to add, which is useful for project deadlines or estimated timelines.
No — every calculation runs locally in your browser. Nothing you enter is uploaded, logged, or stored on any server.
Yes — a due date is simply a start date plus a duration forward, which the calendar-units mode calculates directly. The business-days mode is a full business days calculator on its own, skipping weekends when a deadline is quoted in working days rather than calendar days.

Free Online Date Calculator

Find out what date you land on after adding or subtracting time from a start date. Choose calendar units (days, weeks, months, years) or business days only, and get the exact resulting date and day of the week.

What You Get

  • Add or subtract days, weeks, months, or years from any date
  • Add or subtract business days only, automatically skipping weekends
  • The exact resulting date, including the day of the week
  • A calendar-day count for business-day calculations, so you can see the real-world span including weekends

Who Uses This Calculator

Anyone planning a deadline, estimating a delivery or processing date, counting down to an event, or working out a date a fixed number of business days from today.