Never.

Seriously though. People really should not overcompensate. It is kind of easy to do.

Remember, shooting downhill (or uphill) at a 45 degree angle, 100 yards by the laser rangefinder is like shooting 70 yards flat. That is a pretty steep incline.

Another example would be shooting at 150 yards at a 30 degree angle would be like shooting 130 yards on flat.

The moral is, if you are shooting at only slight uphill or downhill angles, there is very little difference.

The simple formula you can plug into your calculator is:

cosine (angle from flat) X actual distance = distance equivalent if you were shooting flat