About TideCheck

Last updated: March 2026

What is TideCheck?

TideCheck provides tide predictions for over 20,000 stations across >200 countries worldwide. Our predictions are calculated using harmonic constituent analysis — the same proven mathematical method used by national hydrographic offices and maritime agencies around the world.

Each station's tidal signature is decomposed into astronomical components (solar, lunar, and their interactions), which are then recombined to produce tide height predictions at any point in time. This is supplemented by sunrise/sunset, moon phase, and solunar activity data.

What We Build on Top

Raw harmonic constituent data is openly published by government agencies and research institutions. But turning that raw data into accurate, production-ready tide predictions is a significant engineering challenge. TideCheck bridges that gap with:

• A purpose-built prediction engine — our proprietary engine implements 46 tidal constituents with full astronomical correction pipelines, nodal modulation on the 18.6-year lunar cycle, and solar/lunar orbital mechanics. It has zero external dependencies, giving us complete control over accuracy and performance.
• Global station coverage — we merge, deduplicate, and normalize data from three independent sources into a single unified dataset with consistent datums, regions, and metadata across 20,000+ stations.
• Real-time computation — every prediction is calculated on demand at the edge, not served from pre-generated tables. This means flexible date ranges, multiple datum options, and always-fresh results.
• Enriched data — beyond raw tide heights, we compute sunrise/sunset, moon phases, spring/neap conditions, solunar fishing ratings, weather conditions, and activity recommendations — all from a single request.
• Sub-50ms global response times — powered by edge infrastructure that puts computation close to every user worldwide.

TideCheck API

Everything that powers the TideCheck website is available as a developer-friendly REST API. If you're building an app, website, or service that needs tide data, you can skip months of data wrangling, engine development, and infrastructure setup.

• Tide predictions (highs/lows, minute-by-minute time series) for any date range
• Station search by name, coordinates, or proximity
• Sun, moon, solunar, and weather data in a single call
• Multiple datum options (LAT, MLLW, MSL)
• JSON responses with CORS support
• Free tier with 50 requests/day — no credit card required

Explore the API →

Prediction Methodology

TideCheck uses harmonic constituent analysis — the internationally recognized standard method for tidal prediction, as specified by the International Hydrographic Organization (IHO). This is the same fundamental approach used by national hydrographic offices worldwide, including NOAA (United States), SHOM (France), UKHO (United Kingdom), and AHS (Australia).

At its core, the method decomposes the complex rhythm of the tides into individual periodic components — each driven by specific gravitational interactions between the Earth, Moon, and Sun. These components (called harmonic constituents) are combined with high-precision astronomical calculations, including nodal modulation corrections on an 18.6-year lunar cycle, to reconstruct the full tidal signal at any point in time.

Station Types

TideCheck maintains two categories of tide stations:

• Reference stations — Direct harmonic predictions computed from constituent data specific to each location. These provide the highest accuracy.
• Subordinate stations — Predictions derived from a nearby reference station with location-specific time and height corrections applied. TideCheck uses a proprietary interpolation method to produce smooth, continuous tide curves for subordinate stations rather than simple offset tables.

Accuracy & Validation

We continuously validate our predictions against official sources. For US stations, TideCheck predictions typically agree with NOAA's official published predictions to within ±3 minutes in timing and ±2 cm in height — well within the variability caused by weather and atmospheric conditions on any given day.

It's worth understanding what tidal predictions represent: they model the astronomical tide — the predictable, gravitationally-driven component of water level. On a calm day, this is remarkably accurate. However, actual water levels are also influenced by:

• Meteorological effects — wind, atmospheric pressure, and storm surge can shift water levels by tens of centimeters or more
• Seasonal & climatic factors — river discharge, ocean currents, thermal expansion, and long-term sea level trends
• Local geography — shallow water, estuaries, harbours, and complex coastlines can amplify or dampen tidal signals in ways that purely harmonic models approximate

No harmonic prediction — including those from official government agencies — accounts for these real-time variables. For this reason, our predictions are designed for planning coastal activities (surfing, fishing, diving, beach visits) and are not intended for navigation. See our Disclaimer for full details.

How Far Ahead Are Predictions Accurate?

Because harmonic analysis is based on astronomy — which is deterministic and predictable — tidal predictions maintain their accuracy years into the future. The astronomical forces driving the tides follow precise, known cycles. A prediction for next week is essentially as accurate as one for a year from now, assuming stable local conditions.

The main source of long-term drift is gradual sea level change and shifts in local bathymetry, which occur over decades rather than days. For practical planning purposes, our predictions are reliable for any date within the current year and well beyond.

Datums & Reference Levels

Tide heights are meaningless without a reference level. TideCheck supports three internationally recognized vertical datums:

• LAT (Lowest Astronomical Tide) — the IHO international standard, used on most nautical charts worldwide. Under normal conditions, the tide will not fall below this level.
• MLLW (Mean Lower Low Water) — the US tidal datum standard, representing the average height of the lower of each day's two low tides over a 19-year epoch.
• MSL (Mean Sea Level) — the arithmetic mean of hourly water levels observed over a full tidal cycle. Often used as a global baseline.

You can switch between datums on any station page using the datum selector. All times are displayed in each station's local timezone.

Supplementary Data

Beyond tide predictions, TideCheck computes a range of supplementary data for each station:

• Sun data — precise sunrise and sunset times for each day and location
• Moon data — moon phase, illumination percentage, and upcoming lunar phase calendar computed using high-accuracy astronomical algorithms
• Tidal conditions — spring/neap classification based on lunar phase geometry, plus tidal strength ratings
• Solunar forecast — daily fishing quality ratings (1–5 stars) derived from the relationship between lunar position, moon phase, and tidal patterns

Data Sources & Attribution

We are committed to transparency about where our underlying data comes from. TideCheck's harmonic constituent data is sourced from three respected institutions:

NOAA CO-OPS (United States)

Harmonic constituents for US coastal stations are sourced from the NOAA Center for Operational Oceanographic Products and Services (CO-OPS). Includes both reference stations (direct harmonic prediction) and subordinate stations (time/height corrections applied to a nearby reference station).

TICON-4 (International)

International tidal constituents are sourced from the TICON-4 (Tidal Constituents from Observations and Numerical models) database, published by SHOM (Service Hydrographique et Océanographique de la Marine). Licensed under CC-BY-4.0. DOI: 10.17882/109129.

Citation: Lefèvre F., Carre H., Faucher C. (2025). TICON-4 Tidal Constituents from observations and numerical models. SEANOE.

FES2022 (Global Ocean Tide Model)

Additional stations in underserved regions are derived from the FES2022 (Finite Element Solution) global ocean tide atlas, distributed by AVISO+ / CNES. FES2022 provides harmonic constituents on a 1/30° global grid; we extract constituents at specific coastal locations using bilinear interpolation.

Generated using AVISO+ Products. FES2022 was produced by Noveltis, Legos and CLS and distributed by AVISO+.

Contact

For questions, corrections, or data source inquiries, please visit our Contact page.