The greatest tidal ranges occur during spring tides, when the sun, moon, and Earth align at new moon and full moon phases. These tides happen roughly twice per lunar month, year-round. But the absolute largest tidal ranges happen when this alignment coincides with the moon being at its closest point to Earth, an event that occurs six to eight times per year.
How the Moon and Sun Create Spring Tides
Tides are driven by the gravitational pull of both the moon and the sun on Earth’s oceans. Most of the time, these two forces pull at different angles, partially canceling each other out. But twice each lunar month, at the new moon and full moon, the sun, moon, and Earth fall into a roughly straight line (an arrangement called syzygy). In this position, the gravitational attractions of the moon and sun reinforce each other. The combined tidal force produces higher high tides and lower low tides than average, stretching the tidal range to its widest.
The term “spring tide” has nothing to do with the season. It comes from an old meaning of “spring” as a welling up of water. Spring tides occur all year long.
The opposite pattern, called a neap tide, happens during the first and third quarter moon phases, when the sun and moon pull at right angles to each other. Neap tides produce the smallest tidal ranges.
Perigean Spring Tides: The Biggest Regular Events
The moon’s orbit around Earth is not a perfect circle. Once roughly every 28 days, the moon reaches perigee, its closest approach to Earth. When perigee happens to fall near a new or full moon, the result is a perigean spring tide, the largest tidal swings most coastlines experience on a regular basis.
This close-approach alignment occurs six to eight times a year. During a perigean spring tide, high tides are commonly more than a foot higher than high tides during spring tides that fall when the moon is farther away. In places with already dramatic tides, the effect is amplified. Anchorage, Alaska, which sees a tidal range over 30 feet, can experience an additional 3 feet or more on top of that during perigean spring tides compared to spring tides at the moon’s farthest point.
These events are sometimes called “king tides,” a popular but non-scientific term for exceptionally high tides. King tides are not a distinct phenomenon. They’re simply the result of perigee and syzygy lining up favorably.
Why Winter Tides Tend to Be the Largest
Earth’s orbit around the sun also plays a role. Around January 2 each year, Earth reaches perihelion, its closest point to the sun. At this distance, the sun’s gravitational influence on tides is slightly stronger, enhancing tidal ranges. When a perigean spring tide falls near perihelion, the three factors stack: lunar alignment, close lunar distance, and close solar distance. This is why many of the year’s most extreme tides happen in December and January.
There is a common belief that tides are especially large around the equinoxes in March and September, and some coastal areas do see notable tides near those dates. But the equinox itself does not create a distinct tidal-boosting mechanism. Any extra height around the equinoxes comes from the same spring tide and perigee factors that operate all year. The timing just occasionally lines up well in spring and fall.
Geography Makes All the Difference
Astronomical forces set the baseline, but the shape of the coastline determines how dramatic tides actually become in any given location. The global average tidal range is about 3 feet. In the open ocean, the difference between high and low tide is even smaller. But certain bays, inlets, and channels amplify tidal energy enormously.
The most extreme example is Canada’s Bay of Fundy, between Nova Scotia and New Brunswick, where the tidal range can reach 53 feet (16 meters). The bay acts like a funnel, narrowing and shallowing as water pushes inland. More importantly, the bay’s natural oscillation period is approximately 12 hours, nearly identical to the time it takes for one full high-to-low tide cycle. This resonance effect is the same principle that lets you slosh water higher and higher in a bathtub by timing your pushes. Each incoming tide reinforces the previous one, building to extraordinary heights.
Other locations with amplified tidal ranges include the Bristol Channel in the United Kingdom, Ungava Bay in northern Quebec, and parts of the coast of northwestern Australia. In all these places, the combination of funnel-shaped geography and favorable water depth creates ranges far beyond what open coastlines experience.
Putting It All Together
If you’re trying to predict when the very largest tidal ranges will occur at a given location, look for the overlap of three conditions: a new or full moon, the moon near perigee, and (for the absolute peak) a date near early January when Earth is closest to the sun. That combination produces the most extreme tides the astronomy can deliver. Layer that onto a coastline with the right shape and depth, and you get the towering tidal swings that draw tourists to places like the Bay of Fundy.
For practical purposes, tide tables published by agencies like NOAA predict these events years in advance. If you live on a low-lying coast or keep a boat in a tidal harbor, perigean spring tides in winter are the dates worth circling on your calendar.