Tide Time Calculator

The Tide Time Calculator predicts the high tide and low tide times for any day from a single known high tide for your location. Tides are governed by the Moon, so once the calculator is anchored to one real tide it can project the rest of the daily cycle — drawing an interactive tide curve, a live tide clock, and a full daily tide table. It works for semi-diurnal, diurnal, and mixed tide coasts.

How the Tide Time Calculator Works

Ocean tides are the rise and fall of sea level caused mainly by the gravitational pull of the Moon, and to a lesser extent the Sun. As the Earth rotates, each coast passes through the tidal bulges raised by the Moon, producing the familiar pattern of high and low water.

The key number is the lunar day — the time between two passes of the Moon overhead. It averages about 24 hours 50 minutes, slightly longer than a solar day because the Moon moves along its orbit while the Earth spins. On a semi-diurnal coast the sea sees two tidal bulges per lunar day, so successive high tides fall about 12 hours 25 minutes apart.

Starting from your reference high tide \(H_0\), the calculator finds every other tide by stepping along this interval, with low tides falling roughly halfway between consecutive highs:

Why You Enter a Known High Tide

The timing of tides is set by the Moon, but the exact minute high water reaches a particular beach also depends on the shape of the coastline, the depth of the water, and local resonance. These local effects shift the tide by a fixed amount that is the same day after day. By anchoring the lunar cycle to one measured high tide for your spot, the calculator absorbs that local offset and produces far more useful times than a generic worldwide formula could.

Types of Tides

On a mixed coast the two daily high tides differ in height — a higher high water and a lower high water. This calculator reproduces that diurnal inequality, which is why the tide curve for a mixed pattern shows two peaks of different heights.

Spring Tides and Neap Tides

When the Sun and Moon line up at new and full Moon, their pull combines to give large spring tides with higher highs and lower lows. When they are at right angles, near the first and last quarter Moon, the smaller neap tides result. These mainly affect tide heights rather than times, so they are outside the scope of this timing calculator — but they explain why tidal range changes through the month.

How to Use This Calculator

1. Find a known high tide: Look up one recent or upcoming high tide for your location from a tide table, harbour authority, or marine forecast.
2. Enter the reference tide: Type that high tide's date and time, and choose your coast's tide pattern (semi-diurnal, diurnal, or mixed).
3. Choose the day to predict: Pick the day you want tides for, or leave it blank to use the reference day.
4. Read the results: Study the tide curve, watch the live tide clock, and use the daily table of high and low tide times.

Accuracy and Limitations

This tool is a timing estimate. It assumes a steady average lunar interval, so it is typically accurate to within a few minutes over a day or two and drifts more over longer spans. It does not predict the height of the tide in feet or metres, and it cannot account for storm surge, atmospheric pressure, or river flow. For navigation, fishing, diving, or any safety-critical decision, always rely on official tide tables for your exact location.

Frequently Asked Questions

How are tide times calculated?

Tides are driven mainly by the Moon. One lunar day lasts about 24 hours 50 minutes, so for a semi-diurnal coast successive high tides are about 12 hours 25 minutes apart. Starting from one known high tide, this calculator steps that interval forward and backward to estimate every high and low tide for the day you choose.

Why do I need to enter a known high tide?

Exact tide times depend on local coastline shape, water depth, and weather, which only a measured tide table captures. By anchoring the lunar cycle to one real high tide for your location, the calculator can project the remaining tides for that area far more accurately than a generic formula.

What is the difference between semi-diurnal, diurnal, and mixed tides?

A semi-diurnal coast has two high tides and two low tides of roughly equal size each day. A diurnal coast has just one high and one low tide per day. A mixed tide has two highs and two lows, but their heights are clearly unequal, producing a higher high water and a lower high water.

How accurate is this tide calculator?

It is a timing estimate based on the average lunar interval, typically accurate to within a handful of minutes over a day or two and drifting more over longer spans. It does not predict tide heights in feet or metres. For navigation or safety-critical decisions, always use official tide tables for your location.

Why does high tide arrive later each day?

The Moon orbits the Earth in the same direction the Earth spins, so each day the Earth must rotate a little extra to catch up to the Moon. That extra rotation takes about 50 minutes, which is why high tide shifts roughly 50 minutes later from one day to the next.

Can I predict tides for next week?

Yes. Choose any day in the Day to predict field and the calculator projects the tides for that date. Because small daily errors accumulate, the further the day is from your reference high tide, the larger the possible drift, so re-anchor with a fresh known tide for best results.

Additional Resources

• Tide - Wikipedia
• NOAA - Tides and Water Levels