Date Calculator
Find the number of days between dates, the date 90 days from today, or how many business days are left before a deadline. This free date calculator does five things on one screen: days between dates (with or without the start date, also in weeks, months and years), adding or subtracting days, weeks, months or years, countdowns and milestones, business days, and exact age. Everything is calculated in your browser and nothing is sent anywhere.
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When to use it
Count the days in a contract, lease or trip
In "Days between dates", enter 2026-03-01 and 2026-08-31 and tick "Include the start date" to get 184 days. Without the start date it is 183 days. The same panel shows the length in weeks, months, and years, months and days.
Set a deadline in business days
In "Business days", the lower box adds business days to a base date. From Friday 2026-10-16, 1 business day later is Monday 2026-10-19. Untick Saturdays if your team works six days a week.
Count down to an exam, launch or trip
"Countdown" shows D-36 for 2026-11-19 when today is 2026-10-14, along with the weeks and days left. The milestone table below lists day 100, day 1,000 and yearly anniversaries from any start date (day 100 from 2026-01-01 is 2026-04-10).
Check an exact age on a given date
"Age" gives the age in completed years on any date, the days since birth and the next birthday. Change "Age on" to find out how old someone was or will be on a specific day.
How to use
- Pick a calculation from the tabs: Days between dates, Add / subtract, Countdown, Business days or Age.
- Enter dates in the date boxes. The "Today" button fills in today's date.
- Adjust options such as "Include the start date", "Treat Saturdays as days off" or "Also skip South Korean public holidays".
- Results update as you type. You can open a tab directly with #biz or #age at the end of the address.
How the calculations work
- Days between dates: By default the result is the end date minus the start date. With "Include the start date" the first day also counts, which adds one. Jan 1 to Jan 10 is 9 days, or 10 days including the start date.
- Adding months and years: If the target month has no such day, the result moves to the last day of that month: Jan 31 + 1 month = Feb 28 (Feb 29 in a leap year) and Feb 29, 2024 + 1 year = Feb 28, 2025. The months breakdown of a date difference uses the same rule.
- Business days: Business days are Monday to Friday. Untick "Treat Saturdays as days off" to count Saturdays too. You can also skip South Korean public holidays for 2025 to 2027; other countries' holidays are not included.
- Age: Age goes up on the birthday. People born on February 29 turn a year older on March 1 in common years and on February 29 in leap years.
- Supported range: Any date from January 1, 0001 to December 31, 9999 in the Gregorian calendar. Dates are handled as whole days, so time zones and daylight saving time never shift a result by one day.
South Korean public holidays included (2025–2027)
These are used only when "Also skip South Korean public holidays" is ticked. Holidays that fall on a Sunday are listed too.
2025 holidays (244 business days)
| Date | Day | Holiday |
|---|---|---|
| Jan 1 | Wed | New Year's Day |
| Jan 27 | Mon | Temporary public holiday |
| Jan 28 | Tue | Seollal (Lunar New Year) holiday |
| Jan 29 | Wed | Seollal (Lunar New Year) |
| Jan 30 | Thu | Seollal (Lunar New Year) holiday |
| Mar 1 | Sat | Independence Movement Day |
| Mar 3 | Mon | Substitute holiday (Independence Movement Day) |
| May 5 | Mon | Children's Day / Buddha's Birthday |
| May 6 | Tue | Substitute holiday (Buddha's Birthday) |
| Jun 3 | Tue | Temporary public holiday (presidential election) |
| Jun 6 | Fri | Memorial Day |
| Aug 15 | Fri | Liberation Day |
| Oct 3 | Fri | National Foundation Day |
| Oct 5 | Sun | Chuseok holiday |
| Oct 6 | Mon | Chuseok |
| Oct 7 | Tue | Chuseok holiday |
| Oct 8 | Wed | Substitute holiday (Chuseok) |
| Oct 9 | Thu | Hangeul Day |
| Dec 25 | Thu | Christmas Day |
2026 holidays (245 business days)
| Date | Day | Holiday |
|---|---|---|
| Jan 1 | Thu | New Year's Day |
| Feb 16 | Mon | Seollal (Lunar New Year) holiday |
| Feb 17 | Tue | Seollal (Lunar New Year) |
| Feb 18 | Wed | Seollal (Lunar New Year) holiday |
| Mar 1 | Sun | Independence Movement Day |
| Mar 2 | Mon | Substitute holiday (Independence Movement Day) |
| May 1 | Fri | Labor Day |
| May 5 | Tue | Children's Day |
| May 24 | Sun | Buddha's Birthday |
| May 25 | Mon | Substitute holiday (Buddha's Birthday) |
| Jun 3 | Wed | Local elections day |
| Jun 6 | Sat | Memorial Day |
| Jul 17 | Fri | Constitution Day |
| Aug 15 | Sat | Liberation Day |
| Aug 17 | Mon | Substitute holiday (Liberation Day) |
| Sep 24 | Thu | Chuseok holiday |
| Sep 25 | Fri | Chuseok |
| Sep 26 | Sat | Chuseok holiday |
| Oct 3 | Sat | National Foundation Day |
| Oct 5 | Mon | Substitute holiday (National Foundation Day) |
| Oct 9 | Fri | Hangeul Day |
| Dec 25 | Fri | Christmas Day |
2027 holidays (246 business days)
| Date | Day | Holiday |
|---|---|---|
| Jan 1 | Fri | New Year's Day |
| Feb 6 | Sat | Seollal (Lunar New Year) holiday |
| Feb 7 | Sun | Seollal (Lunar New Year) |
| Feb 8 | Mon | Seollal (Lunar New Year) holiday |
| Feb 9 | Tue | Substitute holiday (Seollal) |
| Mar 1 | Mon | Independence Movement Day |
| May 1 | Sat | Labor Day |
| May 3 | Mon | Substitute holiday (Labor Day) |
| May 5 | Wed | Children's Day |
| May 13 | Thu | Buddha's Birthday |
| Jun 6 | Sun | Memorial Day |
| Jul 17 | Sat | Constitution Day |
| Jul 19 | Mon | Substitute holiday (Constitution Day) |
| Aug 15 | Sun | Liberation Day |
| Aug 16 | Mon | Substitute holiday (Liberation Day) |
| Sep 14 | Tue | Chuseok holiday |
| Sep 15 | Wed | Chuseok |
| Sep 16 | Thu | Chuseok holiday |
| Oct 3 | Sun | National Foundation Day |
| Oct 4 | Mon | Substitute holiday (National Foundation Day) |
| Oct 9 | Sat | Hangeul Day |
| Oct 11 | Mon | Substitute holiday (Hangeul Day) |
| Dec 25 | Sat | Christmas Day |
| Dec 27 | Mon | Substitute holiday (Christmas Day) |
Sources: Korea AeroSpace Administration almanacs for 2025, 2026 and 2027 (Official Gazette, 2024-06-20, 2025-06-30, 2026-06-29), Ministry of Personnel Management temporary holiday notices (2025-01-27 and 2025-06-03), and Presidential Decree No. 36290 (2026-04-30), which made Labor Day and Constitution Day public holidays from 2026.
Frequently asked questions
How do I count the days between two dates?
Open "Days between dates", enter the start and end dates, and the number of days appears at once. Tick "Include the start date" if the first day should count too. The result is also shown in weeks, in months, and in years, months and days.
What is Jan 31 plus one month?
February has no 31st, so the result is the last day of February: Feb 28, or Feb 29 in a leap year. A note under the result tells you when this happens.
Which holidays are skipped in business days?
Weekends always. If you tick "Also skip South Korean public holidays", South Korean public holidays and substitute holidays from 2025 to 2027 are skipped as well. Holidays of other countries are not included.
Can I count business days outside 2025–2027?
Yes. Outside that range only weekends are skipped, and the result shows a note saying so.
How is age calculated for someone born on February 29?
In common years they turn a year older on March 1, and in leap years on February 29.
How does the countdown count days?
If the target date is today it shows D-Day, one day before it shows D-1, and one day after it shows D+1. In the milestone table the start date is day 1, so day 100 is the start date plus 99 days.
Are my dates sent to a server?
No. All calculations run in this page's script inside your browser, and the holiday list is built into the page, so no outside service is called.
Last checked: October 14, 2026 · Dagochim team