The planets magnetic declination changes all over the globe, from North America, UK, India to Australia. Even if you remained on the magnetic north pole it would change over time, as the geomagnetic north pole moves around.
This means that the angle of 'error' between magnetic north and physical true north varies depending on your location. As even up to date magnetic declination maps are basically out of date as soon as they are printed you can use this NOAA link for your or any magnetic declination calculation.
Magnetic declination map and values
The NOAA magnetic declination value site is OK but if you want to use a google earth map and just click on a location to get your magnetic declination values then click here.
Magnetic declination and Earths geomagnetic reversals
The earths magnetic declination map also varies over time as the Earths magnetic fields and its geomagnetic north pole and south pole seem to wander, we even appear to have had multiple Earth magnetic pole reversal. The Earths geomagnetic reversals and geomagnetic excursions (variation in the magnetic fields strength and other properties) have great effects on the values of the magnetic fields and especially its polarity.
Why do we get Earth magnetic field reversals? Why does the magnetic north pole location move? Why has it happened multiple times? Why do the values change?