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 53 min | — |
| 4 Jan | 8 h 04 min | +11 min |
| 18 Jan | 8 h 36 min | +32 min |
| 1 Feb | 9 h 20 min | +44 min |
| 15 Feb | 10 h 12 min | +52 min |
| 1 Mar | 11 h 08 min | +56 min |
| 20 Mar (equinox) | 12 h 08 min | +60 min |
| 3 Apr | 13 h 15 min | +67 min |
| 1 May | 14 h 58 min | +103 min |
| 1 Jun | 16 h 22 min | +84 min |
| 21 Jun (solstice) | 16 h 38 min | +16 min |
Note: times are approximate and reflect clock time — European clocks spring forward one hour in late March (BST), which is why the mid-April gain looks larger than earlier weeks.
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.