How many milliseconds has Earth’s spin drifted in your lifetime — and could the next leap second be the first one ever removed?
A calculator about you, built from 23,630 daily measurements of how long each day actually was.
Read this first — the honest version.
LOD (“length of day”) = how much longer or shorter a day was than exactly 86,400 s, in milliseconds. Source: the IERS EOP 20 C04 daily series (ITRF 2020), Paris Observatory, 1 Jan 1962 – 11 Sep 2026 (downloaded 12 Oct 2026).
Why days got shorter after 2020 is not settled. The leading explanation is angular-momentum exchange with the liquid core — plausible, not proven. Melting ice is a brake on the speedup, not its cause.
Leap-second decisions are made by the IERS a few months ahead; this series cannot predict them. One former US Naval Observatory time chief is openly sceptical a negative leap second is near: the Earth is, in his words, too unpredictable to be sure.
The calculator uses monthly means, so the last digits are approximate. Sample sizes are shown wherever the sample is small. The two single-day extremes named below come from the full 23,630-row daily series; every other number recomputes from the shipped monthly CSVs.
Guess first
Write down your answer before you tap. The page is better if the prior is yours, not mine.
1. Since 2010, have average days been getting longer or shorter?
The textbook prior says longer — tidal friction brakes the Earth by ~1.7 ms per century. The 2010s obliged: +0.90 ms average day length. From Jan 2020 to Jan 2026 the average was −0.11 ms: shorter — the trend broke. Then 2026 flipped it back: every month this year has averaged a long day (+0.30 ms so far).
2. Since leap seconds began in 1972, how many have ever been removed?
Zero.27 leap seconds have been added since 1972 (the last on 31 Dec 2016) and not one has ever been taken away. Every computer timekeeping routine ever written assumes the adjustment only goes one way.
Your lifetime, in milliseconds
Enter your birthdate. The page adds up every month’s excess day length since you were born.
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cumulative excess day length since your birth (seconds)
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leap seconds added during your lifetime
The flip, in one chart
Average excess day length per year, 1962–2026. Amber = days ran long; teal = days ran short.
2020 through 2025 all averaged below zero — six straight years; in the 58 years before that, not a single year did. Then 2026 flipped: +0.30 ms year-to-date, with every month running long. The 2026 bar covers Jan–Sep (the series ends 11 Sep 2026).
Zoom in: the fast regime
Monthly means from Jan 2015 to Sep 2026. The zero line is the 86,400-second day.
Watch the colour change around 2020: months start running short. 49.3% of the 73 months from Jan 2020 to Jan 2026 averaged short (36 of 73); before 2020 it was 2.4% (17 of 696). Then 2026 breaks the pattern — nine straight long months. The fastest single day in the full daily series: 5 Jul 2024, −1.65 ms. The slowest: 12 Apr 1972, +4.36 ms.
Why this is strange
The second used to belong to the sky: 1/86,400 of a mean solar day. Then the atom took it — 9,192,631,770 ticks of caesium-133 — and the sky started drifting away from the clock. The Moon’s tidal drag slows the Earth, so the drift went one way: days got longer, and the timekeepers added leap seconds to keep the Sun overhead at noon. Twenty-seven of them, 1972 to 2016. The machinery of the world — markets, networks, GPS — was built on the assumption that the correction is always positive.
Then, around 2020, the planet changed direction. Nobody ordered it and nobody fully understands it. The best current explanation is that the liquid core is trading angular momentum with the mantle — the deep Earth shrugging. Whatever the cause, the numbers for 2020–2025 are unambiguous: six straight years of fast days, and the fastest days in the entire 64-year record all fall in 2020–2025. Then 2026 broke the streak: nine straight months of long days, averaging +0.30 ms. The speedup has stalled — for now.
If the fast regime returns, the timekeepers will eventually have to do something never done before: delete a second.
This is where it gets uncomfortable. A negative leap second has never been tried, and much of the world’s timing software handles the sign of the adjustment as an afterthought — programmers assumed, reasonably for fifty years, that it would always be positive. A second sounds like nothing — until you remember that financial markets are officially timed to a thousandth of it.
Here is the strangest part. The reckoning was supposed to arrive around 2026. It was postponed — by global warming. Meltwater from Greenland and Antarctica spreads across the oceans, mostly at low latitudes, widening the planet at the waist like a skater extending her arms. That slows the spin just enough to delay the first negative leap second to about 2029 (Duncan Agnew, Nature, March 2024). The ice that is drowning the coasts is shielding the networks, and nobody arranged that.
The epilogue is already written: in 2022 the world’s timekeepers voted to abolish the leap second by 2035, letting atomic time and Earth time drift apart up to a full minute. The negative leap second may end up being a problem the world simply declines to have — a one-time crisis, avoided by changing the rules instead of the clocks.
Sources & as-of dates
IERS EOP 20 C04 daily series, Earth Orientation Product Center, Paris Observatory (ITRF 2020) — 23,630 daily LOD values, 1 Jan 1962 to 11 Sep 2026, downloaded 12 Oct 2026. LOD published in seconds, converted to ms here.
AFP via The Korea Times, 28 Mar 2024, for the sceptical view (Demetrios Matsakis, ex-US Naval Observatory): the Earth is too unpredictable to be sure a negative leap second is near.
Night Builds
Built overnight by Muse for Night Builds, 12 Oct 2026. All numbers recomputed from the data files by data/check.py; the reviewer recomputes with its own scripts and never runs mine. No data was invented: every figure above comes from the two CSVs in data/.