−2h 10m
lost since the summer solstice (June 21)
The days start getting longer immediately after the winter solstice — around December 21 or 22 in the Northern Hemisphere (June 20 or 21 in the Southern Hemisphere). From that point, each day is a little longer than the last, without exception, all the way through to the summer solstice six months later.
The change is so slow at first that it's almost imperceptible. In the first week after the winter solstice, London gains only about 2–3 minutes of daylight total. But the pace accelerates through January and February, and by the time the spring equinox arrives in late March, days are lengthening by nearly four minutes every day — the fastest rate of the year.
| Date | Approx. day length | Gain vs. previous week |
|---|---|---|
| 21 Dec (solstice) | 7 h 49 min | — |
| 4 Jan | 7 h 59 min | +10 min |
| 18 Jan | 8 h 28 min | +28 min |
| 1 Feb | 9 h 10 min | +42 min |
| 15 Feb | 9 h 59 min | +50 min |
| 1 Mar | 10 h 53 min | +54 min |
| 20 Mar (equinox) | 12 h 08 min | +75 min |
| 3 Apr | 13 h 04 min | +55 min |
| 1 May | 14 h 50 min | +106 min |
| 1 Jun | 16 h 18 min | +89 min |
| 21 Jun (solstice) | 16 h 38 min | +20 min |
Note: day length is sunrise to sunset, so it is unaffected by the clocks going forward — the uneven gains above are the real seasonal rate, which peaks at the equinox and falls away towards the solstice. The 20 March and 1 May rows span longer intervals than the fortnightly rows around them.
The curve of day length through the year follows a sinusoidal pattern — like a smooth wave. At the peaks (solstices), the wave is nearly flat: the rate of change is at its minimum, close to zero. At the midpoints (equinoxes), the wave is steepest: the rate of change is at its maximum.
This is why the weeks immediately after the winter solstice can feel discouraging — even though the days are technically getting longer, the change is barely noticeable. But February and March bring a rapid shift: by mid-March you are gaining nearly four minutes per day in London, and the evenings start to feel meaningfully longer week by week.
Even though the days start getting longer immediately after the winter solstice, the coldest temperatures of the year typically arrive in January and February — well after the solstice. This is called the seasonal lag. The land, oceans, and lower atmosphere take time to release the cold they have accumulated over autumn and early winter. It takes weeks of gradually increasing sunlight before the net energy balance shifts and temperatures begin to rise.
The same lag works in reverse at the other end: the hottest days of the year usually arrive in July and August, a month or more after the summer solstice.
In the Southern Hemisphere, the same process applies — but offset by six months. Days start getting longer after the June solstice (around June 21), reach their fastest rate of increase at the September equinox, and peak at the December solstice. If you are in Sydney or Cape Town, the period from July to December is your equivalent of the Northern Hemisphere's January to June.
Use the tool on the homepage to see exactly how long today's day is at your location — and watch the year-chart to visualise how the days are growing or shrinking from where you are right now. You can also check sunset today and sunrise today for your location.
There is a reason the days can feel like they are lengthening before the solstice has even passed. The turning point for the evenings comes first.
In London the earliest sunset falls around 12 December, over a week ahead of the solstice, while the latest sunrise does not arrive until about 30 December. For the three weeks in between, sunset creeps later every day while sunrise also keeps getting later. Anyone who mostly notices the light at the end of the working day will register the change well before Christmas; anyone who notices it on the way to work will not feel it until well into January.
The mechanism is the equation of time — solar noon drifting against clock time by up to about sixteen minutes across the year, because the Earth's orbit is an ellipse and its axis is tilted. December is where that drift is steepest, so the two ends of the day come apart most visibly.
Numbers on a page understate how the change feels, because human perception of daylight is tied to specific moments — leaving work, walking the dog, the light at breakfast — rather than to a total. A few landmarks for the latitude of Britain and Denmark:
The clocks going forward in late March adds an apparent hour of evening light overnight, which lands on top of an already steep curve. That combination is why early spring feels so abrupt.
Day length follows something close to a sine wave through the year, and a sine wave changes fastest in the middle and slowest at the extremes. That is the whole explanation for why late December feels stuck and late March feels like a transformation: the solstices sit at the flat top and bottom of the curve, the equinoxes at the steepest part of the climb.
Latitude sets how tall the wave is, and therefore how steep the steep part gets. Near the equator the annual change is a matter of minutes, so there is no perceptible "days getting longer" season at all. At the latitude of Copenhagen the swing is over ten hours, and the March gain is correspondingly dramatic. Inside the Arctic Circle the transition is more dramatic still — the sun returns after weeks of absence and then gains ground extraordinarily quickly. You can see the shape of all of this on the year chart.
The return of the light is not only a matter of convenience. Daylight is the dominant signal that keeps the human circadian system aligned, and morning light in particular is what anchors it. At high latitudes the winter shortage is severe enough to be clinically relevant — seasonal affective disorder is markedly more common the further from the equator you go, and light therapy, which works by supplying a bright morning signal artificially, is a standard treatment.
This is also part of why the timing of the gain matters as much as the amount. Through January and February the extra daylight is arriving mostly in the evening, while sunrise stays late; the morning light that the body clock responds to most strongly does not really return until March. It is a reasonable explanation for why February can feel harder than December despite being objectively brighter.
Day length starts increasing immediately after the December solstice, around 21 December in the northern hemisphere. Sunset, however, starts getting later around 12 December — over a week earlier — because of the equation of time.
It varies through the season. Just after the solstice the gain is under a minute a day. By mid-January it is two to three minutes, and around the March equinox it peaks at three to four minutes a day at the latitude of Britain and Denmark — roughly half an hour a week.
Because most of the early gain arrives in the evening while sunrise stays late, and because the solstice sits at the flat bottom of the annual curve where change is slowest. The morning light the body clock responds to most strongly does not really return until March.