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Date Calculator

Count days between dates — including business days — or add and subtract days from any date

Date Calculation

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Quick summary

Two modes: count the days between two dates (with weeks, business days, and a years-months-days breakdown), or add or subtract days from a date to find a deadline and its weekday. The count excludes the start date and includes the end date. Business days count Monday–Friday only; public holidays are not excluded because they vary by country and employer.

Reviewed by Simple Calculators TeamLast reviewed

How to use this calculator

  1. Choose a mode from the menu at the top: "Days between two dates" or "Add or subtract days from a date".
  2. For days between dates, enter the Start Date and the End Date. The order does not matter — the calculator always reports a positive span.
  3. For add or subtract, enter the Date to start from, then type a number in Days to Add (negative subtracts) — for example 90, or −30 to go back 30 days.
  4. Read the result: the total days with the Weeks + Days, Business Days, and Calendar Span boxes, or the resulting date and its weekday.
  5. If your rule counts both the first and last day (common for rentals and some contracts), add 1 to the total; subtract any public holidays from Business Days yourself.

Date Calculation Formulas

Days Between Two Dates

Days=End Date−Start Date,Weeks=⌊Days7⌋, remainder=Days mod 7\text{Days} = \text{End Date} - \text{Start Date}, \quad \text{Weeks} = \left\lfloor \frac{\text{Days}}{7} \right\rfloor,\ \text{remainder} = \text{Days} \bmod 7
Days
Calendar days, excluding the start date and including the end date
Weeks
Complete weeks in the span
remainder
Days left over after the complete weeks

Worked example

January 1, 2026 to December 25, 2026

Given
Start Date = 2026-01-01
End Date = 2026-12-25
Calculation
Days=358,⌊3587⌋=51, 358 mod 7=1\text{Days} = 358, \quad \left\lfloor \frac{358}{7} \right\rfloor = 51,\ 358 \bmod 7 = 1
Result
358 days = 51 weeks 1 day = 11 months 24 days; 256 business days

Add or Subtract Days

Result Date=Date+n days\text{Result Date} = \text{Date} + n \text{ days}
Date
The starting date
n
Days to Add — a negative number subtracts

Worked example

90 days after March 1, 2026

Given
Date = 2026-03-01
n = 90
Calculation
Mar 1+30 (to Mar 31)+30 (to Apr 30)+30 (to May 30)\text{Mar 1} + 30\ (\text{to Mar 31}) + 30\ (\text{to Apr 30}) + 30\ (\text{to May 30})
Result
May 30, 2026 (a Saturday)

Frequently asked questions

How do I count the days between two dates?

Subtract the earlier date from the later one. This calculator excludes the start date and includes the end date, so Monday to the next Monday is 7 days. If you need both endpoints counted, as many rentals, leases, and medication schedules do, add 1 to the result. You can enter the dates in either order.

How many days are there between January 1 and December 25?

In 2026 there are 358 days from January 1 to December 25, which is 51 weeks and 1 day, or 11 months and 24 days. Of those, 256 are business days (Monday–Friday), before subtracting any public holidays. Leap years add one more day to any span that includes February 29.

What are business days, and how are they counted here?

Business days are Monday through Friday. The calculator counts weekdays after the start date up to and including the end date, so Monday to the next Monday is 5 business days. Public holidays are not removed because they vary by country, state, and employer — subtract them yourself for exact deadlines.

What date is 30, 60, or 90 days from a given date?

Choose "Add or subtract days from a date", enter the starting Date, and type the number of days. For example, 90 days after March 1, 2026 is May 30, 2026, a Saturday. The calculator moves by whole calendar days and shows the weekday, so you can see when a deadline lands on a weekend.

How do I subtract days from a date?

Enter a negative number in Days to Add (negative subtracts). For example, entering −30 with a Date of March 31 gives the date 30 days earlier. This is useful for working back from an event to a booking, notice, or filing deadline. You can add or subtract up to 100,000 days.

Is 30 days the same as one month?

No. Months range from 28 to 31 days, so "30 days" and "1 month" often land on different dates. Adding a calendar month usually keeps the same day number next month, while adding 30 days counts exactly 30 calendar days. This calculator adds days, so use it when a rule says "within 30 days".

Why do the week and month breakdowns differ?

Weeks are always 7 days, but months are 28 to 31 days long, so the same span splits differently. January 1 to December 25, 2026 is 358 days: exactly 51 weeks and 1 day, but 11 months and 24 days in calendar terms. The month breakdown depends on which months the span crosses.

Key terms

Business Day
A weekday (Mon–Fri). Contract and legal deadlines often count business rather than calendar days.
Inclusive vs Exclusive Counting
Whether the start and end dates themselves count — off-by-one errors in deadlines usually trace to this.
Calendar Month Arithmetic
Adding months keeps the day-of-month where possible (Jan 31 + 1 month = Feb 28/29), unlike adding fixed days.

Methodology, sources & limitations

This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.

For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.