How Many Seconds Are There in a Day, Month and Year?

There are 86,400 seconds in a day, 604,800 seconds in a week, 31,536,000 seconds in a common year and 31,622,400 seconds in a leap year. A month has no single answer: 2,419,200 seconds in a 28-day February, 2,505,600 in a 29-day February, 2,592,000 in a 30-day month and 2,678,400 in a 31-day month. Every one of those numbers comes from the same building block, the 86,400 seconds in a day, so once you have that the rest is one multiplication.

Seconds in a day: the arithmetic

A day is 24 hours, an hour is 60 minutes, and a minute is 60 seconds. Multiply the chain:

24 × 60 × 60 = 86,400 seconds

In two steps: 60 × 60 = 3,600 seconds in an hour, then 3,600 × 24 = 86,400. Half a day is 43,200 seconds.

How many seconds are there in a month?

This is the one people actually search for, and the honest answer is that it depends on which month. Calendar months run from 28 to 31 days, so multiply 86,400 by the number of days:

If a question just says “a month” with no month named, the convention is to use 30 days, giving 2,592,000 seconds. That is what most homework answers and finance formulas assume.

For a true average month, divide a year by 12. A common year gives 31,536,000 ÷ 12 = 2,628,000 seconds. Using the Gregorian average year of 365.2425 days, the average month is 30.436875 days = 2,629,746 seconds.

Seconds in a year, week and other units

A common year is 365 days: 365 × 86,400 = 31,536,000 seconds. A leap year adds one more day, so 366 × 86,400 = 31,622,400 seconds.

A useful estimation trick: a year is about π × 10⁷ seconds. That is 31,415,927, within 0.4% of 31,536,000, and physicists use it constantly for back-of-the-envelope work.

A leap year is any year divisible by 4, except century years, which must also be divisible by 400. So 2024 and 2000 were leap years, 1900 was not, which is why the Gregorian average is 365.2425 days and not 365.25.

What one second actually is

All of the above assumes a fixed second. Since 1967 the second has not been defined by the Earth at all. The SI second is defined by an atomic transition:

One second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

That is the number a caesium atomic clock counts. It was chosen to match the astronomical second as closely as measurement then allowed, so nothing in the table above changed when it was adopted.

Why leap seconds exist, and why they end by 2035

The Earth is not a good clock. Tidal friction from the Moon slows its rotation over long periods, and the length of a day wobbles by a millisecond or so because of ocean, atmosphere and core effects. Atomic time does not wobble, so the two drift apart.

The fix since 1972 has been the leap second: an extra second inserted into UTC, usually on 30 June or 31 December, to keep clock time within 0.9 seconds of the Earth’s actual rotation. Twenty-seven leap seconds have been added since 1972, the most recent on 31 December 2016, which is why atomic time (TAI) now runs 37 seconds ahead of UTC.

Those insertions cause real trouble. A minute with 61 seconds in it has crashed servers, broken timestamps and upset satellite navigation and power-grid systems, and the Earth’s recent slight speeding up raised the prospect of a negative leap second that almost no software has been tested against. In November 2022 the General Conference on Weights and Measures (CGPM) voted to stop inserting leap seconds by or before 2035, letting UTC drift from solar time and correcting the accumulated difference in one much larger step much later.

So for the numbers on this page: a day is 86,400 seconds, except on the rare day that carried a leap second and ran 86,401 seconds long. After 2035 that exception is expected to disappear.

FAQs

How many seconds are there in a month?

It depends on the month’s length. A 28-day February has 2,419,200 seconds, a 29-day February has 2,505,600, a 30-day month has 2,592,000 and a 31-day month has 2,678,400. When no specific month is given, the usual convention is 30 days, which is 2,592,000 seconds.

How many seconds are there in a day?

86,400 seconds. The working is 24 hours × 60 minutes × 60 seconds. Along the way, an hour is 3,600 seconds, half a day is 43,200 seconds and a week is 604,800 seconds.

How many seconds are in a year?

A common year of 365 days has 31,536,000 seconds, and a leap year of 366 days has 31,622,400 seconds, a difference of exactly one day or 86,400 seconds. Using the Gregorian average year of 365.2425 days, the figure is 31,556,952 seconds.

Is a day always exactly 86,400 seconds long?

Almost always. The Earth’s rotation varies by about a millisecond a day, so UTC has occasionally been given a leap second, making that day 86,401 seconds long. Twenty-seven such seconds were added between 1972 and 2016. The CGPM decided in 2022 to phase leap seconds out by or before 2035.

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