The Bay of Mont Saint-Michel sees two high tides and two low tides each day, with a tidal range that can reach roughly fourteen metres on the biggest cycles. That puts it among the largest tidal ranges in continental Europe. All times on this site are computed for the Saint-Malo reference port and adjusted for the bay.
Why the range is so dramatic
The bay funnels the Atlantic tide off the English Channel into a shallow, narrowing basin. As the tidal wave compresses, its amplitude grows. When the lunar (M2) and solar (S2) tidal forces line up at full moon and new moon, they reinforce each other and produce spring tides. The strongest spring tides of the year cluster around the equinoxes in March and September, when the Earth, Moon, and Sun align most precisely with the equator.
Reading the coefficient
Each cycle gets a coefficient on a scale from 20 to 120. Below 95 it is a regular tide: the water comes in and out, retreating further on the higher end of the range. At 95 and above it becomes a spring tide and the entire character of the bay changes. The full year of coefficients sits in the calendar above. Frequently asked questions.
When the Mont becomes an island
The submersible passage to the rock is only fully covered on a handful of days each year. The Office de Tourisme classifies these "Mont becomes an island" days using local bay dynamics rather than a flat coefficient threshold; weather, wind, and atmospheric pressure all push the actual water level above or below prediction. The 2014 footbridge replaced the old causeway and let the sea wash all the way around the rock again on the strongest tides. Read how we classify these days.
Regular tide