Spring and neap tides
A short guide to the two-week cycle that controls how big the tides get.
Tides go up and down twice a day on most of the UK coast. The size of that swing changes through the month. Some days the water swings five metres between low and high. Other days it barely swings two. That difference is the spring/neap cycle.
What a spring tide is
A spring tide is a day when the swing between low water and high water is unusually large. The lows go lower than usual, the highs go higher than usual, and the currents in between run faster.
Springs happen twice a month, around the new moon and the full moon, when the moon and sun line up. Their gravity adds together, so the tidal pull is at its strongest. The name has nothing to do with the season. It comes from the older sense of spring as in the water "springing forth".
What a neap tide is
A neap tide is the opposite. The moon sits at right angles to the sun, around the first and last quarter moons, so their gravity pulls in different directions and partly cancels out. The result is a smaller swing between low and high. The water moves less, the currents are slacker, and there is a longer period of near-still water around high and low tide.
Neaps also come twice a month, midway between the springs.
Why the cycle takes about two weeks
The moon orbits the earth every 29 and a half days. The sun-moon-earth alignment lines up twice in that orbit, once at new moon and once at full moon, with quarter-moons in between. So you get spring, neap, spring, neap, roughly every seven days.
The peak spring usually falls a day or two after the new or full moon, not on it. This lag is normal and comes from the way water in the ocean basins responds to the changing pull.
What it means in practice
On springs:
- Low tide uncovers more beach, sandbars, and rock pools than usual.
- Currents run harder through narrow channels and around headlands.
- Boats moored in tidal harbours rise and fall further between turns.
- Surf can be punchier where the bigger swell of water focuses on a bank.
On neaps:
- Low water doesn't drop as far, so less of the beach is exposed.
- Currents are slacker, which can mean better fishing for some species.
- Tidal harbours stay closer to a constant level, helpful for shallow-draught boats.
How LocalTides labels them
Each station has a year of tide data. We work out the daily range (low to next high, or high to next low, whichever is biggest) and rank every day from 0 to 100 against the rest of the year. Days in the top 15 are flagged as spring. Days in the bottom 15 are flagged as neap. Everything in the middle is normal.
The thresholds are station-specific. A "neap" tide at Bridlington can still have more range than a "spring" at Poole, because the underlying tides are bigger up the East Yorkshire coast than they are in the Solent. The label tells you how the day compares to other days at that location.
A note on safety
These predictions are astronomical. They tell you what the moon and sun do, not what the water will actually be doing on the day. Don't use this site, or any tide table, for sailing, navigation, swimming, fishing, or any decision where the water level matters for safety. Use official sources and a current marine forecast for that.