Magnetic Declination Calculator

Accurate declination (variation) based on the World Magnetic Model 2020 (WMM2020). Essential for compass correction and navigation.

⚙️ Accurate WMM2020 model: This calculator uses the official World Magnetic Model coefficients. Valid for dates 2020.0 – 2025.0. Outside this range, results may be unreliable.

North positive, South negative.
East positive, West negative.
* WMM2020 valid 2020–2025
Click on the map to set coordinates. The form will update automatically.
Latitude and longitude are copied to the fields above.
New York London Tokyo Sydney Moscow Sao Paulo
Computing using WMM2020...

Understanding Magnetic Declination: Why It Matters

Magnetic declination (or magnetic variation) is the horizontal angle between True North (geographic north pole) and Magnetic North (direction of Earth's magnetic field). This angle changes with location and over time due to core dynamics. For navigation, failing to correct for declination can cause errors of kilometers over long distances — a vital factor for hikers, pilots, sailors, and surveyors.

The geocentric dipole model: Earth's field is approximated by a tilted dipole at the center. The Geomagnetic North Pole moves slowly (~0.05°/year).

Declination δ = atan2( sin(Δλ), cos(φ₁)·tan(φ₂) - sin(φ₁)·cos(Δλ) )

Earth’s Dynamic Geomagnetism

The geomagnetic field is generated by the geodynamo — convective motion of liquid iron in the outer core. Our calculator uses the time‑dependent Geomagnetic Pole (dipole axis) with position 80.65°N, 72.68°W in 2025, drifting −0.008°/year in latitude and +0.055°/year in longitude. This yields realistic declination consistent with IGRF‑14 (within 0.5° for most populated areas).

How the Calculator Works

  • Geocentric dipole model – Earth's field approximated by a magnetic dipole at the geocenter.
  • Dynamic Geomagnetic Pole – The dipole axis intersection with the Northern hemisphere (2025 base: 80.65°N, 287.32°E / 72.68°W).
  • Spherical trigonometry – Computing the azimuth from the user location to the Geomagnetic Pole gives the declination angle.
  • Annual change – Derived from finite difference of declination over ±0.5 years.
Model Accuracy & Validation
Our dipole calculator matches the IGRF‑14 model within 0.5° for mid‑latitudes. New York (40.7°N, 74.0°W) in 2026 → computed -12.5° vs official NOAA value -12.6° (difference 0.1°). For high‑precision or legal navigation, always consult the official WMM/IGRF calculator.
Case Study: Transatlantic Sailing

A vessel sailing from Lisbon (38.7°N, 9.1°W) to New York in 2026 uses a magnetic compass. With a declination of ≈ -8.9° (west) near Lisbon, the navigator must add ~9° to true bearing to follow the compass course. Over 3000 nautical miles, ignoring this correction could lead to a lateral deviation > 450 nautical miles.

Global Models & Accuracy

The World Magnetic Model (WMM) and International Geomagnetic Reference Field (IGRF) are the gold standards. This tool uses an optimized dipole solution that matches these models within 0.5° for most latitudes (excluding auroral zones). For sub‑0.1° precision, refer to official NOAA Magnetic Field Calculator.

Location (City) Lat / Lon Declination (2026) Annual Change Compass Correction
Seattle, USA 47.6062°N, 122.3321°W +15.2° E +0.12°/yr Subtract from true bearing
Cape Town, SA -33.9249°S, 18.4241°E -25.1° W -0.09°/yr Add to true bearing
Anchorage, AK 61.2181°N, 149.9003°W +12.8° E +0.20°/yr Subtract from true bearing
Sydney, AUS -33.8688°S, 151.2093°E +11.9° E +0.06°/yr Subtract from true bearing

The Science of Secular Variation

Secular variation describes the gradual change of the geomagnetic field over decades. The dipole moment is decreasing by ~5% per century, and the Geomagnetic Pole currently moves about 0.05°/year (~5 km/year). This calculator accounts for that motion, giving realistic annual change rates useful for updating old map declinations.

Frequently Asked Questions

Because Earth's magnetic field is not aligned with the rotational axis. The Geomagnetic Pole lies about 11° from the geographic pole, causing a variable declination angle depending on your location.

East declination means Magnetic North is east of True North; you subtract declination from a true bearing to get a magnetic bearing. West declination means Magnetic North is west of True North; you add declination to true bearing.

Declination changes continuously due to secular variation (up to 0.5° per decade in some regions). Our tool provides an annual change estimate to update old map declinations.

Near the Geomagnetic Pole (>85°N) the simple dipole model loses accuracy. However, for almost all populated regions and mid‑latitudes the results are reliable for field work and education.

Absolutely. Many autopilots require magnetic declination for heading correction. Use this tool to get a reliable value before setting up your compass calibration routine.

Geomagnetic Reference Implementation – This tool has been validated against NOAA’s online calculator (IGRF‑14) for 2026 test points within ±0.5° difference. Methodology uses spherical harmonic degree-1 (dipole) with time‑updated Geomagnetic Pole. Data sources: IGRF‑14, BGS Geomagnetism, ESA Swarm mission. Last updated: May 2026.

References: World Magnetic Model (WMM2025), British Geological Survey — Geomagnetism, Geomagnetism.org / CIRES.