UK Tidal API Frequently Asked Questions

UK Tidal API Technical FAQs
Tidal Theory FAQs

UK Tidal API Technical FAQs

Q: Can I extract the predicted height of tide for a station at a specified time and date?
A: Yes. The Foundation and Premium UK Tidal API subscriptions allow users to extract predictions for a specific date and time. The Discovery UK Tidal API provides High Water and Low Water event information.

Q: How much data can I get through the API?
A: As a maximum, the Premium UK Tidal API allows the user to extract up to a year’s worth of both historical and future tidal predictions, with as little as 1-minute intervals.

Q: Can I access other information via an API?
A: Currently only tidal predictions are supplied in an API format. If you require additional information via an API or have any feedback, please contact

Q: I haven’t received my verification email. How can I verify my email address?
A: Firstly, check your spam and junk folder. If it's not in there or your inbox, please contact

Q: Can I store or cache the data?
A: If you are using the Foundation or Premium UK Tidal API subscription, caching is permitted. Caching is not permitted if using the free of charge Discovery UK Tidal API subscription. This is because storing the data in any kind is in breach of Copyright law.

Q: Is British Summer Time applied to predictions?
A: No. All predicted height times are shown at Greenwich Mean Time (GMT). For information on when the clocks change please visit

Q: Are the Lat and Long returned the wrong way?
A: The standard the UKHO adheres to is ISO 6709 - Standard representation of geographic point location by coordinates (Latitude before Longitude).
However, the standard format for geoJSON is that point coordinates are in x, y order (longitude, latitude for geographic coordinates). To avoid confusion the UK Tidal API adheres to the standard geoJSON format.

Q: Can I get Tidal data for the Channel Islands?
A: Unfortunately, data for the Channel Island Stations are not currently included within the Tidal API. For predictions not included within the UK Tidal API please visit to find other tidal products available.

Q: Why do I need to obtain a copyright licence?
A: All work the UKHO creates is protected by Crown copyright and/or database rights in the UK, and it is also protected elsewhere in the world through international treaties. Any reproduction, translation or adaption of UKHO material requires an official UKHO Copyright licence.

Q: How do I know if I qualify for a free of charge copyright licence?
A: You can check if you qualify for a free of charge copyright licence by checking the qualifying criteria

Tidal Theory FAQs

Q: Some Tidal Stations are not returning low water date and time information?
A: For Some Ports, for example Rye Harbour, where the Low Water times and Heights are not available, it is not possible to generate a set of predicted times or heights of Low Waters.
This is because the location is in an environment where certain tidal events are either difficult or impossible to observe (usually Low Waters.) For example, the location ‘dries out’ at Low Water, or is located up-river where only the river water flow is prevalent at Low Water until the next High Water arrives.
Therefore, there is limited prediction output that can be generated at such locations. For the same reasons, it is also not possible to generate a continuous predicted curve at this location.

Q: Some Tidal Stations are returning 4 high water times for one day?
A: Some ports are affected by ‘ double High Waters ’ and ‘ High Water Stands’.
These affect the ‘usual-shape’ of the tidal curve, causing it to become somewhat distorted. The reasons for the distortions are caused by particular complexities in the tidal regime (shallow water effects) on the fundamental harmonic constituents (the underlying variables upon which the tide is predicted) causing the shape of the predicted curve to be so affected. This effect is prevalent along a stretch of the south coast of England, approximately from Start Point to Portland, and in the Solent the effects are particularly marked.

Q: How are tides predicted?
A: First the behaviour of the tide has to be recorded by a tide gauge at each particular location and the results subsequently analysed. The results of the analysis, known as tidal constants, are then used in a computer program to predict the behaviour of the tide for any period required.

Q: I am interested in mean tidal levels as opposed to predictions - where can I obtain these?
A: All volumes of ADMIRALTY Tide Tables contain mean tidal levels at locations for which we hold the necessary tidal data. They can be purchased from any ADMIRALTY Distributor listed at How To Buy.

Q: Why is my local harbour not available?
A: Tidal predictions can only be computed for locations at which there are tidal data that have been derived from the analysis of the tidal observations. If no tidal observations have been taken at your particular location then, unfortunately, no tidal predictions can be computed.

Q: How often do tides occur?
A: There are three types of tidal regime.
Diurnal tides are those where one High and one Low Water occur during a period of 24 hours mainly experienced in the Pacific Ocean.
Semi-Diurnal tides are characterised by having two High and Low Waters in a 24-hour period mainly experienced in the Atlantic Ocean.
Mixed tides are where the tidal regime exhibits characteristics of both Diurnal and Semi Diurnal tides experienced in areas such as the Indian Ocean, Gulf of Mexico, and Australia.