Magnetic declination calculator
A compass points to magnetic north, not true north. Here is the difference where you are, from the official World Magnetic Model.
Using declination with a map and compass
Declination (or "magnetic variation") is the angle between true north and the direction a compass needle points. East declination means the needle points east of true north; west, west of it.
- Map to compass (true to magnetic): subtract east declination, add west declination.
- Compass to map (magnetic to true): add east declination, subtract west declination.
A handy memory aid: "east is least, west is best" — going from true to magnetic, subtract east, add west. Many compasses let you set the declination once so you can read true bearings directly.
Why it changes
The Earth's magnetic field is made by moving molten iron in its outer core, and it drifts. The magnetic north pole has been moving towards Siberia at tens of kilometres a year, so declination changes from year to year — the reason old maps print the declination and its yearly change. Near the magnetic poles compasses become unreliable, and local iron deposits, power lines and steel objects can deflect the needle anywhere.
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Source: World Magnetic Model 2025, US NOAA National Centers for Environmental Information and the British Geological Survey (public domain), valid 2025–2029; our code matches all 100 of NOAA's official test values.