A tide table is one of the most useful bits of paper you can carry on a coastal walk, and one of the easiest to misread. It looks like a tidy grid of numbers, but it is really a forecast of where the sea will be — and how long you have before the beach you are standing on quietly disappears behind you.
What follows is the practical version: what high and low water times actually mean, why springs and neaps matter more than most walkers realise, and how to turn a table into a plan you can trust.
What a tide table actually tells you
Most UK tables list, for each day, the times of high water (HW) and low water (LW) and the predicted height of the sea at those times, in metres. Two highs and two lows a day is typical, roughly twelve and a half hours apart.
Heights are not depths
A line reading LW 08:14, 0.8m means the sea is expected to fall to 0.8 metres above chart datum — the low baseline used for navigation charts. It does not mean the water is 0.8m deep, and it does not mean you can paddle out 0.8m. Depth depends on the seabed under you.
What matters for walking is the range: the gap between high and low. If the day reads HW 14:32 at 4.6m and LW 08:14 at 0.8m, the range is 3.8m. On a gently sloping sandy beach, that range can expose or swallow hundreds of metres of sand. On a steep rocky shore, the same 3.8m is a narrow strip. Same numbers, very different walk.
Check the time zone
Many tables are printed in GMT, also written UT. In summer, British Summer Time runs an hour ahead. Getting that wrong turns “we'll be back well before high water” into “we're wading”. If a table does not state its time zone, find one that does.
Springs and neaps: why the same walk changes
Roughly twice a month, around the new and full moon, the sun and moon line up and their pull adds together. The range is at its biggest: spring tides. About a week later, at the first and third quarter, the pulls partly cancel and the range is at its smallest: neap tides.
Nothing to do with the season — a spring tide in June is still a spring tide. The word comes from the old sense of the tide “springing up”.
This is the bit that catches people out. A spring low can uncover a causeway, sandbank or route that stays underwater on a neap. A spring high can reach a slipway or a path that is bone dry a week earlier. So the useful question is not “when is low water?” but “how low, and how high?”
Getting figures for your stretch of coast
Tide tables are calculated for standard ports — large harbours with long records. If you are walking somewhere else, you need either a table for a nearby standard port or a secondary port entry, which gives a time difference and a height adjustment to apply to the main port's figures.
Local harbour authorities, national park websites, council pages and sailing clubs often publish tables for smaller places, which is usually more accurate than guessing from the nearest big port. If your walk crosses an estuary or a tidal river mouth, look for a local table specifically.
One more thing: tides run roughly 50 minutes later each day, so a route that worked at 10am on Saturday may need a 10.50am start on Sunday. Tables printed a year in advance are fine, but check you are reading the right date.
The rule of twelfths, in plain numbers
Between low and high water the sea does not rise steadily. It starts slowly, accelerates through the middle, then eases off. The rule of twelfths splits the six hours or so of a rising tide into twelve parts:
- First hour: 1/12 of the range
- Second hour: 2/12
- Third hour: 3/12
- Fourth hour: 3/12
- Fifth hour: 2/12
- Sixth hour: 1/12
With a range of 3.8m, the first hour brings about 0.3m of water and the second about 0.6m. By the end of the fourth hour roughly 2.9m has arrived. Half the water comes in during the middle two hours. That is why a flat sandy inlet can look harmless at 9am and be knee-deep by 11.30am.
Walk out on a falling tide, and turn back while the water is still going down. If the tide has already turned, you are walking against the clock.
Planning a coastal walk around the tide
- Pick your beach or route first, then the tide. Decide which section needs low water — a spit, a causeway, a cave, a river crossing.
- Find the local table and note the heights, not just the times. Write down HW and LW for the day and the range.
- Work out your window. Aim to be on the tidal section within two hours either side of low water, and well clear before the tide has risen much.
- Add a buffer for slower walking. Sand, shingle and mud take longer than a footpath. Children and dogs take longer still.
- Have a plan B. Know the higher path, the inland route or the nearest road, and turn back early rather than pushing on.
- Tell someone your route and expected return, and carry a charged phone. Signal on the coast is patchy, so download an offline map before you leave.
What a tide table can't tell you
Predictions assume calm, average weather. Add a strong onshore wind or low pressure and the sea can run noticeably higher and arrive faster than the table suggests. Storms far out in the Atlantic can send swell onto a beach that is, on paper, perfectly safe.
Local quirks matter too. Estuaries fill from the sides as well as the mouth, so water can appear behind you. Sandbanks shift, channels move, and mud that looked firm at low water can be soft on the return. Rivers and heavy rain can change the picture entirely.
Tide tables are a planning tool, not a guarantee. If a route feels marginal, or the water is moving faster than you expected, turn around. No walk is worth being cut off for.
Before you set off: a five-line check
Note the local HW and LW times and heights. Confirm whether it is a spring or neap tide. Check the wind direction and strength for the day. Identify your turnaround time and stick to it. Tell someone where you are going and when you expect to be back.
Do that and a tide table stops being a set of numbers and becomes what it should be: permission to relax on the coast, knowing exactly how much beach you have.
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