given distance over other distances. It's not exact, but gives you a pretty good idea. Your 10k pace of 10 minutes per mile projects roughly to a 4:50 marathon time. So, finishing at 4:30 or less is not likely unless you do some speed work. Your 10k pace needs to be down around a 9:16 to finish a marathon in 4:30.

There is a lot of truth to what others have said about marathons being slower or "wheels coming off", especially if it is your first. Just focus on finishing the first one.