Depends on the angle.
Whether up/down the distance will be shorter for the bullet.
Therefore if the angle is +/- 30 degrees the real distance the bullet flies is 0.9 of the range indicated. Ie 100m at a 30o angle is the same as shooting at a target at 90 m
At 45o it would be 0.7 ie 70m.
These are good rules of thumb If the angle is less than 20o and the range less than 200 dont worry about the calculations
Mark