Tidal Range Estimator

Frequently Asked Questions

What is the difference between spring and neap tides?

Spring tides (near new and full moon) have the largest range - high tides are higher and low tides are lower. Neap tides (near first and last quarter) have the smallest range - both highs and lows are closer to the mean. The cycle repeats roughly every 14.75 days.

How much bigger is a spring tide than a neap tide?

Using the typical ±25% swing this calculator models, a spring tide can be roughly 65% larger in total range than a neap tide (1.25 vs 0.75 times the mean) - though the exact ratio varies by location.

Does this calculator predict tide times for my harbor?

No - it estimates where a date falls in the spring/neap cycle using your supplied mean tidal range. Real tide times and heights require station-specific harmonic data; always use an official tide table for navigation.

How often do spring tides occur?

Twice per lunar month - once near new moon and once near full moon, about 14.75 days apart. Neap tides fall in between, near the first and last quarter moon.

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Aviation & Marine Disclaimer: Educational only. Not for flight or navigation operations.

This calculator is for educational and informational purposes only and is not a substitute for official flight or navigation planning. Always use current performance charts, an approved POH/AFM, certified navigation tools, official charts, and current weather sources, and follow all applicable FAA, ICAO, USCG, and other regulatory guidance. Do not rely on this tool for real-world flight, marine, or trailering decisions. Verify all results independently before operating any aircraft or vessel.

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How This Calculator Works

Tidal range - the vertical difference between high and low water - is not constant through the month. It swells to a maximum (spring tide) near new and full moon, when the sun and moon align and their tidal pulls add together, and shrinks to a minimum (neap tide) near the first and last quarter, when the sun and moon pull at right angles and partly cancel. This calculator does not predict a specific station's tide times or heights - real tide prediction needs harmonic constituents unique to each station, published in official tide tables. Instead, you supply your own local mean tidal range (from a tide table, chart datum, or cruising guide) and a date, and it estimates where in the roughly 29.5-day spring/neap cycle that date falls and how far the range likely swings from the mean. Pair it with the moon phase calculator for the underlying lunar cycle and the anchor scope calculator to size rode for the tide swing you find here.

Formula / Method

Tide-phase factor = cos(4π × moon-phase fraction), which is +1 at new moon and full moon (spring tide) and −1 at first and last quarter (neap tide) - the factor of 4π (rather than 2π) captures that spring tides recur twice per lunar month, at both new and full moon, not once. Range multiplier = 1 + 0.25 × tide-phase factor, a ±25% swing around the mean range that is typical for many coastal stations (the exact swing varies by location and this is a planning estimate, not a station-specific prediction). Estimated range = mean range × range multiplier. A result is labeled “spring” when the multiplier is at least 1.15, “neap” when it is at most 0.85, and “transitional” in between.

Worked Example

A station with a 4 ft mean tidal range, checked on a new-moon date. Tide-phase factor = cos(0) = 1. Range multiplier = 1 + 0.25 × 1 = 1.25. Estimated range = 4 × 1.25 = 5 ft - a spring tide about 25% above the mean. Checked instead about 7–8 days later, near first quarter: tide-phase factor = cos(2π) ≈ −1. Range multiplier = 1 − 0.25 = 0.75. Estimated range = 4 × 0.75 = 3 ft - a neap tide about 25% below the mean, roughly 40% less total range than the spring tide two weeks prior.

Common Mistakes

Treating this as a substitute for an official tide table - real tide times and heights depend on each station's harmonic constituents (shaped by local coastline geometry and water depth), which this planning-level estimate does not model. Using a mean range from the wrong reference station - tidal range can differ dramatically between two points a short distance apart, especially in bays, inlets, and rivers; always use the mean range for the specific station or the nearest one with similar characteristics. Forgetting that spring tides happen at both new AND full moon - some sailors only think of spring tides at new moon, but the full moon produces an equally large spring tide about two weeks later. Ignoring the added effect of onshore wind and low barometric pressure, both of which raise water level beyond the astronomical tide predicted here.

Tips & FAQ

Where do I find my station's mean tidal range? Official tide tables (NOAA in the US, and equivalent hydrographic agencies elsewhere) publish mean range for every reference and subordinate station. How accurate is this estimate? It is a planning-level approximation of the spring/neap cycle shape, not a substitute for a station-specific tide table - real predictions can differ due to local geography, weather, and river discharge. Why does the range matter for anchoring? A larger tidal swing means more rode needed at low water and more scope to manage at high water - see the anchor scope calculator to size your rode across the swing. Disclaimer: planning study only; always carry current official tide tables for navigation.

Tidal Range Estimator

Frequently Asked Questions

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