Only one number really counts in rationalizing the cost of a fundraising renewal: Your cost of acquisition of a new donor.
Is it worth doing a second renewal mailing? … or a third?
Do the math. Keep sending renewals until the cost of renewing a donor exceeds the cost of acquiring a new donor.
You can rationalize an even greater expense to renew any donor for the first time, of course. The statistical lifetime value of each first-year renewal is immense. Here you might compare the value of someone who doesn’t renew, which is about, uh, nothing.
Acquisition costs are high, with no decline in sight. Do the math when considering any investment in retention, particularly first-year retention.
Oh, and let’s not forget that similar math comes into play when considering welcome kits and other types of acknowledgment.(