Minty- welcome to the forum. When you get a minute, stop by the intro thread, and say howdy.
Lead is going to be influenced by several things- flight time of the bullet, relative motion of a moving target (moving at 90 degrees, 45 degrees, etc), speed of movement, and one of the MOST important- wind.
Click here for a link to the Winchester ballistic calculator- it allow you to select caliber, bullet type and weight, range, and gives you holdover, offset for wind, and flight time.
FWIW, a deer moving at a right angle to you moving at a slow walk, shot will offset about 6 inches. Quartering towards or away, about half that. But a 10 mph wind, typical 30-06, will move over 6 inches- IF that wind is at a right angle to bullet path.