Attrition Is Your Enemy
It is something that should be measured monthly. If it is around 40%, you should be concerned. Over 50% to 60%, you need to worry about it. Over 60%, you have a serious problem.
It costs 4½ times the resources, energy, and time to get a new gift than to renew one.
Your job is to have an effective program of stewardship— letting your donors know how important they are to you.