Magnetic Declination Calculator

Magnetic declination is the horizontal angle between true north (the direction of the geographic North Pole) and magnetic north (the direction a compass needle points), measured at your location. It is expressed in degrees East or West — for example "12° W" means magnetic north lies 12° west of true north.

Declination is the horizontal angle between true north and magnetic north and depends on where you are on Earth. Inclination (magnetic dip) is the vertical angle the field makes with the horizontal — about 0° at the magnetic equator and nearly 90° (straight down) near the magnetic poles. Deviation is completely different: it is the error a compass shows because of magnetic material near the compass itself (a car, a phone, a steel ship), not a property of the location.

Use: true bearing = magnetic bearing + declination, counting easterly declination as positive and westerly as negative. So with 10° E declination, a magnetic bearing of 45° becomes a true bearing of 55°. With 10° W declination it becomes 35°. To go the other way: magnetic bearing = true bearing − declination.

"East" means magnetic north is east of true north (positive declination, e.g. +12.8° in Sydney); "West" means magnetic north is west of true north (negative declination, e.g. −12.5° in New York). The sign convention used by navigators and by this calculator is: East positive, West negative.

Earth's magnetic field is generated by moving molten iron in the outer core, so the field pattern drifts — this slow drift is called secular variation. Most places see declination change by a few hundredths of a degree per year (for example about +0.02°/yr in Jakarta and +0.17°/yr in London in 2026). This calculator applies the WMM2025 secular-variation coefficients, so it also reports the annual change for your date.

WMM2025 is the World Magnetic Model for 2025–2030, published by NOAA (USA) and the British Geological Survey (UK). It represents Earth's main magnetic field as 168 spherical-harmonic coefficients plus their yearly rates of change. In most populated areas its declination is accurate to roughly half a degree to one degree. Near the magnetic poles the horizontal field is very weak and compass directions become unreliable — the model flags that regime.

WMM2025 is officially valid from 13 November 2024 to 31 December 2029. Inside that window the secular-variation (annual change) model keeps results accurate. Outside the window the tool still computes a value by linear extrapolation, but it warns you that accuracy degrades the further you go.

The agonic line is the line on the map where magnetic declination is exactly zero — true north and magnetic north coincide there. It currently runs roughly through parts of the Americas and western Europe/Africa, and it moves slowly westward over the years as the field drifts.

Barely. The field weakens slightly with height, but at the altitudes people normally work at (even on mountains or in aircraft at 10 km) the declination changes by only a few hundredths of a degree. This calculator accepts an altitude input and evaluates the model at that height above the WGS84 ellipsoid for completeness.

True north points to the geographic North Pole (Earth's rotation axis). Magnetic north is where your compass points — currently in the Canadian Arctic and moving. Grid north is the "up" direction of a map projection grid (e.g. UTM) and differs from true north by the meridian convergence. Compass work corrects magnetic → true with declination; map work corrects grid → true with convergence.