Enter the declination at the start of the year, the annual change in declination, and the number of years since the start of the year into the calculator to determine the magnetic variation. This calculator can also evaluate any of the variables given the others are known.

Magnetic Variation Formula

The following formula is used to calculate the magnetic variation.

MV = D + (M * Y)

Variables:

  • MV is the magnetic variation (degrees) D is the declination at the start of the year (degrees) M is the annual change in declination (degrees per year) Y is the number of years since the start of the year

To calculate the magnetic variation, multiply the annual change in declination by the number of years since the start of the year. Add this result to the declination at the start of the year. The result is the magnetic variation.

What is a Magnetic Variation?

Magnetic variation, also known as magnetic declination, is the angle between magnetic north and true north at a particular location. It is the result of the Earth’s complex and ever-changing magnetic field. This variation is important to consider in navigation and compass-based activities, as it can cause a significant difference between the compass bearing and the actual geographic direction. The value of magnetic variation changes depending on where you are on the Earth and also changes slowly over time.

How to Calculate Magnetic Variation?

The following steps outline how to calculate the Magnetic Variation.


  1. First, determine the declination at the start of the year (D) in degrees.
  2. Next, determine the annual change in declination (M) in degrees per year.
  3. Next, determine the number of years since the start of the year (Y).
  4. Next, gather the formula from above = MV = D + (M * Y).
  5. Finally, calculate the Magnetic Variation (MV).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

declination at the start of the year (D) = 10 degrees

annual change in declination (M) = 2 degrees per year

number of years since the start of the year (Y) = 5 years