Your compass does not point to true north, and the error is always changing.

Countries & Cities · Published 10 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Magnetic declination is the angle between the direction your compass needle points and the geographic North Pole. Because Earth's magnetic field is generated by shifting flows deep within the planet, this angle varies by location and drifts over time. Relying on a static map without adjusting for it can lead you astray.

Magnetic declination, also known as magnetic variation, represents the difference between magnetic north—the direction a compass needle follows—and true north, which points toward the geographic North Pole. By convention, this angle is expressed in degrees and minutes, with positive values indicating magnetic north lies to the east of true north, and negative values indicating it lies to the west. Lines of equal declination across the Earth's surface are called isogonic lines, while areas where the declination is zero are marked by agonic lines.

The phenomenon is driven by the complex, irregular flows of molten material deep within the Earth. Because these internal flows are constantly evolving, the magnetic field is in a state of secular change. This means that at any given point on the planet, the declination is not fixed; it drifts slowly over time. While this shift might be as subtle as two degrees per century in some regions, it can be much more rapid near the poles. For instance, the declination at Ivujivik can change by one degree every three years.

Navigation requires careful correction for these variations. A compass adjusted for a specific declination will provide true north bearings, but only as long as the user remains within that same isogonic zone. For precise work, navigators use models like the World Magnetic Model (WMM) or the International Geomagnetic Reference Field (IGRF) to predict current values. These models account for the core-mantle boundary dynamics, though they may be supplemented by crust-aware models like the Enhanced Magnetic Model to account for local magnetic anomalies caused by iron ore or magnetite deposits in the Earth's crust.

It is vital to distinguish declination from magnetic deviation, which is a localized error induced by nearby metallic objects like the iron on a ship or aircraft. When calculating a true bearing, one must account for both the magnetic variation of the Earth and the specific deviation of the vessel. Navigators often use the mnemonic 'West is best, East is least' to remember whether to add or subtract these values when converting between compass, magnetic, and true bearings.

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