It depends on a number of factors:
Location - where was the body while it was decomposing. Bodies have remained fairly intact in cold bogs or extremely hot deserts because there are fewer parasites to feed off them
State of Body - a dismembered body will decompose faster than one that is totally extant. A body that has had it's internal organs removed will decompose less quickly than one that still has them (no acids to eat away from the insides - mummification)
Apparell - the clothing on the body helps to protect - more & tighter clothing equals slower decomposition.
Storage Type - bodies buried without any type of protection will not survive as long as bodies in coffins. Bodies in wooden coffins will decompose faster than bodies in stone coffins.
Depth of burial - deeper = slower (cooler temperatures)
there may be other factors, but those are the ones that come to mind.