Date Calculator — Days Between Any Two Dates

Enter Parameters

Adjust sliders or type values directly

Start Date

End Date

Or Add / Subtract Days (+/-)

days

Real-time Calculation Ready

Adjust parameters to see instant results

AI Summary & Key Formula

Date Calculator Quick Reference

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Quick Answer

A date calculator counts the calendar days between two dates by subtracting the earlier date from the later one, and can also add or subtract a number of days from a start date. For example, 1 January 2026 to 15 September 2026 is 257 days (36 weeks and 5 days, about 8.4 months), and 90 days after 1 March 2026 is 30 May 2026. Use it for deadlines, notice periods and contract terms; the end date is not counted, months are averaged at 30.44 days, and business days are an estimate (5/7 of the total) that ignores public holidays.

How This Calculation Works

Values calculate dynamically in real-time as you enter figures or adjust sliders.
The equation on the right is exactly what the calculator runs — check any result by hand.

Core Equation

Date Difference:
  Days = |End Date − Start Date| (calendar days; the end date is not counted)
  Weeks = floor(Days / 7), remainder in days
  Months ≈ Days / 30.4375
  Business Days ≈ round(Days × 5 / 7) (estimate; public holidays not excluded)

Date Addition:
  Result = Start Date + N days (N may be negative)

How to Use the Date Calculator

Quick 3-step guide for accurate and fast calculations

STEP 01

Enter your start date

In the Date Calculator, fill in Start Date, End Date and Or Add / Subtract Days (+/-).

STEP 02

Read your difference in total days

The Date Calculator instantly shows Difference in Total Days, Difference in Weeks & Days, Difference in Approximate Months and Resulting Date (Start + Days), updating as you type.

STEP 03

Compare scenarios

Change End Date to see how it affects Difference in Total Days, then check the formula below to verify the math.

Specific Instructions:

Enter a start date and an end date to get the number of days between them, shown as total days, weeks and days, approximate months and estimated business days. To find a date in the future or past, enter a number of days in the add/subtract field (use a negative number to go back); the resulting date is counted from the start date.

Date Calculator Formula

The Date Calculator uses the following formula, calculated in your browser as you change the inputs:

Date Difference: Days = |End Date − Start Date| (calendar days; the end date is not counted) Weeks = floor(Days / 7), remainder in days Months ≈ Days / 30.4375 Business Days ≈ round(Days × 5 / 7) (estimate; public holidays not excluded) Date Addition: Result = Start Date + N days (N may be negative)

Sources:

Worked Example: Date Calculator

Start: January 1, 2026 | End: September 15, 2026 Calendar days = 257 days Weeks = 36 weeks, 5 days Add 90 days to March 1, 2026 → May 30, 2026

Calculations run in your browser — your inputs are never stored on our servers.Formula sources & methodology

Frequently Asked Questions — Date Calculator

How many days between two dates?

To count days between two dates, this calculator subtracts the earlier date from the later date. For example, from January 1 to December 31 of the same year is 364 days (365 in a leap year). The result includes both start and end dates only if you count both endpoints.

What date is 30 days from today?

Enter today's date as the start date and 30 in the add/subtract days field. The calculator returns the calendar date 30 days later, handling month lengths and leap years for you. For example, 30 days after 31 January 2026 is 2 March 2026, because February 2026 has only 28 days, and 30 days after 26 September 2026 is 26 October 2026. Enter −30 instead to find the date 30 days earlier.

How do I calculate business days only?

The calculator gives an estimate: it takes the total calendar days and multiplies by 5/7, which assumes weekends make up two of every seven days. For example, 26 September to 25 December 2026 is 90 days, or about 64 business days. It does not remove public holidays, and a short range can be off by a day or two depending on which weekdays it starts and ends on, so count precisely when a legal deadline depends on it.