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Longest Day of the Year Calculator

How long the longest day actually lasts at your latitude, how many minutes more daylight that is than at the equinox, the ten longest days of the year and the month-by-month curve — June solstice in the north, December in the south.

Related tools

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Day of the Year CalculatorThe ordinal day number of any date — the ISO 8601 ordinal format — with the days remaining, the ISO week, the quarter, the weekday, the percentage of the year elapsed, and the month-by-month addition shown in full.Day of Year CalendarA full year on one page: twelve month blocks where every cell carries its day-of-year number from 1 to 365 or 366, today highlighted, and each date's ISO week, quarter and days remaining one click away.Shortest Day of the Year CalculatorHow little daylight the shortest day leaves at your latitude, how many minutes less that is than at the equinox, polar night counted day by day, and the ten shortest days of the year — December solstice in the north, June in the south.Birth Day of the Week CalculatorFind the weekday you were born on, the weekday of your next birthdays, which weekdays repeat most, and the Doomsday rule behind it.First Day of Autumn CalculatorThe exact instant autumn begins — September equinox in the north, March equinox in the south — and how many minutes of daylight your latitude loses each day at that moment, the fastest rate of the year.First Day of Spring CalculatorThe exact instant spring begins in either hemisphere — March equinox in the north, September equinox in the south — in UTC and in your own offset, with the astronomical and meteorological start side by side and the next ten years.First Day of Summer CalculatorThe exact instant summer begins — June solstice in the north, December solstice in the south — plus the latitude above which the Sun never sets and why summer is the longest astronomical season.First Day of Winter CalculatorThe exact instant winter begins — December solstice in the north, June solstice in the south — why it is the shortest astronomical season, and why meteorological winter straddles two calendar years.

Longest Day of the Year Calculator works straight from this page — free, instant, nothing to install. You will find it under Dates & time, with Day of the Year Calculator and Day of Year Calendar for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Longest Day of the Year Calculator?

How long the longest day actually lasts at your latitude, how many minutes more daylight that is than at the equinox, the ten longest days of the year and the month-by-month curve — June solstice in the north, December in the south.

When would I actually use this?

Answering a scheduling question exactly: how many working days until a deadline, what date falls sixty days out, and what time that is for a colleague elsewhere.

What is the most common mistake?

Counting days by subtracting dates and forgetting whether the endpoints are included. Inclusive and exclusive counts differ by one, which is the difference between meeting a deadline and missing it.

How is Longest Day of the Year Calculator different from Day of the Year Calculator?

They sit next to each other but answer different questions: Day of the Year Calculator is the one to open when you need it to the ordinal day number of any date — the ISO 8601 ordinal format — with the days remaining, the ISO week, the quarter, the weekday, the percentage of the year elapsed, and the month-by-month addition shown in full. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Day of Year Calendar is the closest one after this: A full year on one page: twelve month blocks where every cell carries its day-of-year number from 1 to 365 or 366, today highlighted, and each date's ISO week, quarter and days remaining one click away.

What else is worth having open alongside it?

Shortest Day of the Year Calculator and Birth Day of the Week Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Calendar arithmetic follows the proleptic Gregorian calendar and the IANA time-zone database, so daylight-saving transitions and leap years are handled. Public holidays vary by country and region and are not assumed.

Further reading

All guides →
ExplainerDate Arithmetic Is Harder Than It Looks"One month later" has no single correct answer, and every date library has had to pick one. Month addition is neither associative nor invertible, a day is not always 24 hours, and age is not days divided by 365.25.ExplainerLeap Years: The Rule, the Exception, and the Exception to the ExceptionDivisible by four, except centuries, except centuries divisible by four hundred. The three-line rule exists because the tropical year is not 365.25 days, and the arithmetic behind it explains ten deleted days in 1582 and a calendar that repeats exactly every 400 years.How-toCountdown to New Year: How to Count the Days and Weeks LeftBuilding a countdown to a target date is just counting whole days from today to the target, then splitting that total into weeks. Learn the method with a worked example.ExplainerWhat Generation Am I? Birth-Year Cutoffs ExplainedBoomer, Gen X, Millennial, Gen Z or Alpha? Learn the commonly used birth-year ranges, why the boundaries are fuzzy, and how to place yourself if you were born near a cutoff.ExplainerHow Many Working Days Are There in a Year?A year has roughly 260 weekdays before holidays. Learn where that number comes from, why it varies by country, and how public holidays bring it down to the working days you actually get.ExplainerWhat Is a Leap Year? The /4, /100, /400 Rule ExplainedWhy some years have a February 29, how the divisible-by-4, -100 and -400 rules combine, and how to check any year quickly.