Date tools.

Date Calculators

Timezone-aware date calculations

Last updated recently. The calculator catalog and featured countdown links are refreshed during the normal site update cycle so the entry points stay relevant.

CALCULATORS

Pick the right tool

Days Between Dates

Count days, weeks, and months between two dates

Days Until a Date

Count days remaining until a future date

Add or Subtract Days

Find the date N days before or after a given date

Age Calculator

Calculate exact age in years, months, and days

Day of the Week

Find what day of the week any date falls on

Business Days

Count working days between two dates (excludes weekends)

How to calculate a date difference or add and subtract days

Use the date calculator hub to count the days between two dates, or to shift a start date forward or backward by a number of days.

Choose the date calculator you need
Pick a calculator tile: days-between for the gap between two dates, days-until or days-since for a countdown or count-up to a single date, add-days to shift a date, business-days for working days only, or age, what-day, and week-number for the related calculations.
Enter your dates
On the calculator page, enter the start date and either the end date or the number of days to add or subtract. Days-between needs two dates; add-days needs one date plus a day count and a forward or backward direction.
Read the result
The calculator updates instantly. Date-difference tools return a whole-day count; add-days returns the resulting calendar date. All math runs on calendar dates, so leap years and daylight-saving changes never skew the answer.

Tool evidence

Date-math methods covered by this hub

The date-calculator hub now explains the calculation family behind each tool before sending the user into a specific live calculator.

3/3 checks

Whole calendar days

Verified

Days-between, days-until, and days-since use calendar-date differences rather than elapsed milliseconds, so daylight-saving hours do not skew the count.

Gregorian basis

Verified

Add/subtract-day and age calculations are framed around the proleptic Gregorian calendar, including leap years and uneven month lengths.

ISO week rules

Verified

Week-number links and copy call out the ISO first-Thursday rule instead of treating week numbering as a vague locale preference.

Practical use cases

Deadline math

Use days-between or business-days for contracts, content calendars, and project timelines where the unit is the calendar day.

Personal date lookups

Use age, what-day, and week-number tools when the answer is a calendar label rather than a duration.

Trust boundaries

Holidays are separate: Business-day math skips weekends by default. Public-holiday exclusions need an explicit holiday set or country-specific calendar.

POPULAR COUNTDOWNS

Countdowns people keep coming back to

Christmas 2026 New Year's Eve 2026 Thanksgiving 2026 Halloween 2026 Independence Day 2026 Diwali 2026

What this hub calculates

The date-math methods, and how each is computed

This hub is a launcher for date calculations that fall into a few distinct families. Each part below explains the generic method; open any calculator tile above for that calculation's live inputs and worked examples.

Date difference

Days-between, days-until, and days-since all measure the same thing — the number of whole calendar days separating two dates. The count is done on calendar dates rather than elapsed milliseconds, so daylight-saving changes and leap days never throw the result off by an hour.

Add and subtract days

Add-days shifts a start date forward or backward by a fixed number of days and returns the resulting calendar date. It steps through the Gregorian calendar, so month lengths and leap years are handled automatically — adding 30 days to January 31 lands in early March, not on an impossible February date.

Business days

The business-days calculator counts only Monday through Friday between two dates, skipping weekends. It answers deadline questions — "ten working days from today" — that a plain calendar count gets wrong. Public holidays are not auto-excluded unless a calculation specifies a holiday set.

Age, weekday, and week number

Age converts a date difference into years, months, and days. What-day returns the weekday a given date falls on. Week-number reports the ISO 8601 week (1 to 52 or 53), where week 1 is the week containing the year's first Thursday and weeks start on Monday.

Every calculator here works on calendar dates in the proleptic Gregorian calendar, so leap years and uneven month lengths are handled automatically. Counts use whole calendar days rather than elapsed time, which keeps results stable across daylight-saving changes.

Date-calculator method

How we calculate this: Date-difference tools count whole calendar days between two dates; add-days steps a date forward or backward through the Gregorian calendar; business-days counts Monday-to-Friday only; age converts a difference into years, months, and days; what-day returns the weekday; week-number applies ISO 8601 week rules. All math runs on calendar dates rather than elapsed milliseconds, so leap years and daylight-saving changes do not skew the result.
Data sources: Calculations follow the proleptic Gregorian calendar and, for week numbers, the ISO 8601 week-date standard (week 1 contains the year's first Thursday; weeks start on Monday). Date math uses the date-fns library.
Update cadence: The calculator catalog revalidates daily. The calculation logic is fixed by the Gregorian calendar and ISO 8601, so it does not change between releases; only the featured links are refreshed.

Reference data for the date calculator

Reference fields include the date-difference, add/subtract-days, business-days, age, what-day, and week-number calculation families, the Gregorian calendar basis, and the ISO 8601 week-numbering rule.

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FAQ

What can I calculate here?: This hub brings together days-between, days-until, business-day, age, add-days, and week-number tools so the next date-math step is one click away.
Is this page only for countdowns?: No. The countdown links are just one entry point. The main purpose of this page is to help people choose the right date calculator quickly.

Related planning pages

Date math often turns into timezone, countdown, or meeting-planning work once the first answer is clear.

Countdown hub

Browse event pages when the date question is really about a public release or live event.

Timezone converter

Use timezone conversion once a date calculation becomes a cross-city scheduling problem.

Meeting planner

Move into overlap planning after you know the date and need the right hour.

Browse countdown pages

Use the human-readable browse layer when you want stronger event-led date pages quickly.

How to calculate a date difference or add and subtract days

Use the date calculator hub to count the days between two dates, or to shift a start date forward or backward by a number of days.

Choose the date calculator you need

Pick a calculator tile: days-between for the gap between two dates, days-until or days-since for a countdown or count-up to a single date, add-days to shift a date, business-days for working days only, or age, what-day, and week-number for the related calculations.

Enter your dates

On the calculator page, enter the start date and either the end date or the number of days to add or subtract. Days-between needs two dates; add-days needs one date plus a day count and a forward or backward direction.

Read the result

The calculator updates instantly. Date-difference tools return a whole-day count; add-days returns the resulting calendar date. All math runs on calendar dates, so leap years and daylight-saving changes never skew the answer.

The date-math methods, and how each is computed

Date difference

Add and subtract days

Business days

Age, weekday, and week number

FAQ

What can I calculate here?

This hub brings together days-between, days-until, business-day, age, add-days, and week-number tools so the next date-math step is one click away.

Is this page only for countdowns?

No. The countdown links are just one entry point. The main purpose of this page is to help people choose the right date calculator quickly.

Date Calculators