Magnetic Variation (MagVar) Calculator

Charts may have outdated magnetic variation (declination) information shown on the compass rose. It becomes less accurate beyond five years from the year shown. The automatic MagVar map included in your GPS or chart-plotter system may have several degrees of error. You can get an up-to-date value from NOAA.


NOAA's National Centers for Environmental Information has a calculator here:
Magnetic Declination Estimated Value.

• The WMM 2020 App

Or, you can download the NOAA app, WMM2020, which allows you to obtain the MagVar for any location: no Internet required.

Depending on your browser, you may be asked, "Would you like to save this file?" [] If so, click 'Save File'. The file will normally be downloaded to your 'Downloads' directory. Unzip the file in a directory of your choosing. To use, click on the file WMMGUI.exe.

NOTE: This application only runs under Windows®

Depending on your version of Windows and your settings, it should open a similar window to the one shown on the left. The 'Help' feature provides clear instructions for its use. The calculated MagVar will appear in the window under 'Declination', indicated by the red outline.

Due to the unpredictable, changing nature of Earth's magnetic field, the World Magnetic Model is revised every 5 years, and good for the 4 years following the year shown on the window header. However, unexpected changes in the magnetic field may necessitate interim revisions of the model.

For Summer 2023 in Cape Breton, a value of 17°W is suggested.

Revised: 2023-03-15

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