When does the tide turn?
High and low water times, plus a 24-hour tide curve, for coastal spots around the UK.
Today at Croyde, Devon
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In — · —
Today’s tidesM2 model · approximate
A working model, not gospel — the sea has its own moods, wind and pressure shift things by 30 minutes either way.
M2 harmonic model · per-port phase offset · reviewed May 2026
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The tide is the most predictable thing in nature and the most local thing in nature, at once. The maths is straightforward, the inputs are anything but. Here’s what’s under the hood — and what it can’t see.
One harmonic, not all of them.
UK tides are a sum of dozens of harmonic constituents — the dance of the moon, the sun, the shape of the basin. We use just the dominant one: M2, the principal lunar semidiurnal, period 12 hours and 25.2 minutes. That’s the rhythm that makes UK coasts have two tides a day, about 50 minutes later each day.
Each port has its own phase.
High water doesn’t happen at the same time everywhere. The wave sweeps round Britain on a roughly 12-hour clock, hitting the south-west first, the east coast hours later, Scotland later still. Every port in the list has an M2 phase offset (relative to Dover) baked in, so the times shift by location, not just date.
Spring and neap come from the moon.
Twice a month, the sun and moon line up — full and new moons — and you get the biggest tides (springs). In between, they pull at right angles and the range squashes (neaps). We model that as a smooth 14.77-day envelope on the tidal range. Spring days swing the full range; neap days swing roughly half.
The curve is the same maths, drawn.
The 24-hour graph isn’t separate data — it’s the same M2 sinusoid sampled every ten minutes and rendered as an SVG. The dots are the high- and low-water turning points; the dashed line is now. Everything is computed in the browser, no server, no API.
The ones we get asked.
Why are my local times slightly different to this?
Three reasons, in order of how much they’d move the number. One, we only model M2 — for a fully accurate prediction you’d add about a dozen more constituents (S2 sun-driven, N2 lunar elliptic, K1, O1, M4 shallow-water, and so on). That’s why the official tide tables can differ by 10–20 minutes from ours, especially in shallow estuaries.
Two, weather. A southerly gale and low pressure in the Atlantic can shift the time of high water at Brixham by half an hour and the height by half a metre.
Three, the spot you care about may be a few miles from the port we use. The Bristol Channel changes minute-by-minute over short distances. If timing matters, find a chart for the nearest standard port.
What’s the difference between a spring tide and a high tide?
Easy to muddle. A high tide happens twice a day, every day — it’s just the peak of any tidal cycle. A spring tide is a specific kind of cycle: the days around new or full moon, when high water is higher than usual and low water is lower than usual. So a spring tide gives you a higher high and a lower low. Neaps are the opposite — less movement, more middling. The word “spring” here has nothing to do with the season; it’s an old word for “leap” or “jump”.
Best tide for surfing? For swimming?
Surfing: depends on the spot. Most UK beach breaks work best on the push from low to mid tide. Reef breaks often want a specific window. The picker can’t tell you what suits your local — ask the surf shop or watch a session before you commit.
Wild swimming: high water is usually safest at coastal spots, especially anywhere with sand bars, channels, or cut-off bays. The water’s deepest, currents are at their slackest around the turn of the tide, and you’re less likely to be racing the sea on the way out.
I want to walk a tidal causeway. Is your tool good enough?
No. For St Michael’s Mount, the Holy Island causeway, Worm’s Head, the Burry Inlet — anywhere where being on the wrong side of high water is dangerous — use the official tide tables for that specific crossing. The local council or trust usually publishes safe-crossing times, which account for the geography in a way a single-harmonic model never will. Treat our tool as “rough planning”, not navigation.
My spot isn’t in the list. Will you add it?
The list is curated rather than comprehensive — standard ports and well-known surf and swim spots, with reliable phase data. If you have a spot you think should be in there, drop us a note (the Contact link in the nav). For other spots, find the nearest standard port on the list; the times will be within 15–20 minutes for most of the surrounding coast.
What does “tidal range” actually mean?
The vertical distance between high water and low water on a given tide. A 5-metre range means the sea drops 5 metres between high and low — which on a gently sloping beach can expose hundreds of metres of sand. UK ranges are dramatic: a 12-metre range in the Severn is among the biggest in the world. The Mediterranean barely manages 30 centimetres.