Exact Day Length* — Thu, 5 Apr 2018
Today's prediction: 24 hours, 0 minutes, 0.0007488 seconds (0.7488 milliseconds)
Yesterday's prediction: 24 hours, 0 minutes, 0.0008971 seconds (0.8971 milliseconds)
At the start of today, UT1 was 0.1296063 seconds ahead of UTC.
Modern timekeeping defines a day as the sum of 24 hours – but that is not quite correct. The Earth's rotation slows down over time. So in terms of solar time, most days are a little longer than 24 hours.
How Long Is Today?
Today is predicted to be 0.7488 ms (milliseconds) or 0.0007488 seconds longer than 24 hours. This is the time it takes Earth to rotate 34.83 cm (13.71 in), as measured at the equator.
This means that today lasts:
24.0000002080 hours or
24 hours and 0.75 ms
On average, a mean solar day in the last 365 days was 0.92 ms over 24 hours, so today's day length is below average. Over this period, 233 days have been longer than today, while 133 have been shorter than today.
If every day was as long as today, a leap second would have to be added every 1335.47 days.
Today's Day Length* in Context
Day length Date
Yesterday24 hours +0.90 msWed, 4 Apr 2018
Today24 hours +0.75 msThu, 5 Apr 2018
Tomorrow24 hours +0.65 msFri, 6 Apr 2018
Shortest 201824 hours -0.55 msThu, 26 Jul 2018
Longest 201824 hours +4.60 msWed, 4 Jul 2018
Last Year Average24 hours +1.03 msYear 2017
* Yesterday's, today's and future day lengths are predictions.
Average Day Lengths & Leap Seconds
In rare cases, a day can also be shorter than 24 hours. The last time this happened was on Mon, 18 Jul 2016 (day was 0.03 ms short). However, the average day exceeds 24 hours. See the table below for yearly average day lengths.
To make up for the additional duration, leap seconds are added to our clocks from time to time.
Average Solar Day Length
Year Average day Total yearly excessLeap second added
2018+0.74 ms269.26 ms-
2017+1.03 ms375.02 ms-
2016+1.34 ms490.76 ms31 Dec
2015+1.25 ms458.03 ms30 Jun
2014+0.99 ms362.96 ms-
2013+1.02 ms373.99 ms-
* Current year's average day length and total yearly excess are predicted.
Why Are the Days Getting Longer?
The speed of the Earth's rotation decreases over time, but it also varies from day to day. One of the main factors are the celestial bodies surrounding us. For example, the Moon's gravitational pull causes tides and changes the Earth's shape, ultimately resulting in a lower rotational speed. The distance between Earth and Moon changes constantly, which makes for daily variations in the speed our planet rotates around its own axis.