How to Read a Tide Chart: NOAA Tide Predictions, MLLW and Spring Tides
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How we wrote this: A plain-English summary of NOAA's tide prediction user guide and National Ocean Service tide explainers, checked October 29, 2026. Predictions are astronomical only; check the local forecast for storm surge and surf.
Timing a beach day, a tide-pool walk or a sandcastle build starts with the tide. NOAA publishes free predictions for 3,000+ locations along the U.S. coast. Here is how to read them.
Find your station
On NOAA Tides & Currents, pick a station from the map, a state list, or by name, ID or coordinates. NOAA's user guide explains two kinds:
- Harmonic stations have long-term data and their own harmonic constants, so predictions can be produced for any interval (hourly, 15- or 6-minute).
- Subordinate stations were shorter-term. Their predictions are adjustments of a nearby harmonic station's high and low tides only, so times between highs and lows are approximations.
Read the numbers
NOAA's default display, per the user guide, is:
- Times in local time with daylight saving adjustments (LST/LDT). You can change the time zone.
- Heights in feet relative to Mean Lower Low Water (MLLW). NOAA's datum page defines MLLW as the average of the lower low water height of each tidal day over the National Tidal Datum Epoch. So a low of 0.0 ft is right at that average, and a negative height (for example −1.2 ft) means the water is predicted to drop below it. Note the time of the next high before you walk out.
- High/low list or a curve. The list gives the turning points; the curve shows the water in between.
Why the times shift each day
NOAA explains that a lunar day is 24 hours and 50 minutes, so most coasts see two highs and two lows in that span, with highs about 12 hours 25 minutes apart. That's why tomorrow's high tide comes roughly 50 minutes later than today's. Always read your own station's list rather than assuming a fixed pattern.
Spring and neap tides
- Spring tides (popularly "king tides" when extreme) come at new and full moon, when the Sun and Moon line up and the tidal range is larger. The name has nothing to do with the season.
- Neap tides come about seven days later, at first and third quarter, when highs are a little lower and lows a little higher.
See our Moon phases guide and full moon dates.
What predictions leave out
NOAA says its predictions don't include other influences such as storm surge or sea level rise. Check the NWS forecast, and our guides to beach weather safety and rip currents, before going out on a low tide.