Calquly
Time & Date

Date Calculator

Three things people need from a date calculator: how far apart two dates are, what date lands a certain distance away, and the same again counting working days only.

This calculator needs JavaScript to run. The formula, the worked examples and the explanations below all work without it.

Dates are handled as plain calendar dates, so time zones cannot shift the answer by a day.

Inclusive or exclusive: the question that changes the answer

Ask how many days are between 1 January and 31 January and you can defensibly answer 30 or 31. Both are right; they answer different questions.

  • Exclusive (30 days) counts the elapsed time — how many midnights pass. This is what you want for deadlines, interest, notice periods and age.
  • Inclusive (31 days) counts every calendar day the range touches, start day included. This is what you want for holidays, hotel stays, event lengths and "how many days am I away for".

The checkbox on the first tab switches between them, and the steps underneath the result spell out which one produced the number.

Adding months is not the same as adding 30 days

Months have different lengths, so "one month later" has to be defined. The convention almost everyone uses — including this calculator, banks and contract law in most places — is to keep the same day number in the next month, and to clamp to the last day when that day does not exist.

So 31 January plus one month is 28 February (or 29 in a leap year), not 3 March. The calculator says so explicitly in the steps whenever a clamp happens.

Order matters: years and months are applied first, then weeks and days. 31 January + 1 month + 1 day gives 1 March, while + 1 day + 1 month gives 1 March too — but 31 January + 1 month + 2 days gives 2 March, which is not what a naive 30-day step produces.

Business days

The business-day tools count Monday to Friday and skip Saturday and Sunday. That covers the standard working week in most of the world, and it is what "5 business days" means on almost every shipping and banking page.

What they deliberately do not do is skip public holidays. There is no single list — US federal holidays differ from state holidays, which differ from UK bank holidays, which differ again by year. A calculator that silently picked one country's list would give a confidently wrong answer to everyone else, so this one tells you what it counted and lets you subtract holidays yourself.

An order ships in 5 business days from Friday 11 September 2026.

Monday the 14th is day 1, so day 5 is Friday 18 September. Seven calendar days, five working ones.

Worked examples

How many days between 1 January 2026 and 31 January 2026?

30 elapsed days, or 31 if you count both endpoints. Of those, 22 are weekdays.

What date is 90 days after 8 September 2026?

7 December 2026. Using "3 months" instead would give 8 December — a day apart, which matters for a contract.

What was the date 45 days ago from 8 September 2026?

25 July 2026.

Common uses

  • Contracts and notice periods: 30, 60 and 90-day deadlines.
  • Project planning: working out a due date from a start date.
  • Travel: counting nights versus days, and visa duration limits.
  • Shipping and returns: when a business-day window actually closes.
  • Personal countdowns: days until an event.

If one of your dates is a birth date, the age calculator gives a friendlier breakdown.

Frequently asked questions

How many days are between two dates?
Subtract the earlier date from the later one to get elapsed days. Add one if you want to count both the start and end day — the checkbox does it for you and the steps say which method produced the number.
Does the calculator handle leap years?
Yes, using the full Gregorian rule: divisible by 4, except century years unless they are divisible by 400. February 2024 had 29 days, February 1900 had 28. Dates are converted to a day number for the arithmetic, so leap days are never approximated.
What happens when I add a month to 31 January?
You get 28 February, or 29 in a leap year. The day number is clamped to the last day of the target month rather than spilling into March, which matches how contracts, subscriptions and billing cycles are normally interpreted.
Are public holidays included in business days?
No. Weekends are skipped, holidays are not, because holiday lists differ by country, state and year. The result tells you how many calendar days it covered so you can subtract any holidays that apply to you.
Does my time zone affect the result?
No. Dates are treated as plain calendar dates rather than moments in time, which is the whole reason a lot of date calculators are off by one for users far from UTC. Nothing here converts through a timestamp.
Can I enter the end date before the start date?
Yes. The difference tab swaps them and tells you it did, so you always get a positive count rather than a confusing negative one.