For planning purposes, I give donors a “shelf life” of 5 years. In other words, I assume 100% turnover of my entire donor base every five years .

Immediately you say–not true! I have a board member who has been with me for 17 years! I’ve got donors who have been around since the 80s!

Setting aside why you have a board member who’s been there for 17 years, let’s take a look at those people. When was the last time they increased their gift? What new donors have they brought in in the past 3 years (or decade). How much of your stewardship time are they demanding, for what return?

I’m not advocating dismissing these people, and there will be exceptions to the rule–longtime donors and volunteers who continue to deliver.

But you shouldn’t count on them.

If you have a development program operating on the assumption of high turnover, you’re going to be constantly watching for opportunities to acquire new faces (and therefore new gifts). You’re going to take care of your new donors, which is going to impress them. You’ll never be destroyed by the “sudden” loss of a major gift, because there will always be another one in the pipeline.

Assuming a short giving arc also keeps you on top of trends in giving. And donors are very very susceptible to trends. Some are led by societal forces, some by world events (for instance 8 years ago, when many large donors transferred all their giving to tsunami relief after the Boxing Day disaster). Sometimes major foundations like Gates, MacArthur, or Wallace will trigger systemic changes in giving through large initiatives. If you’re constantly relying on a few long-time donors, or assuming that all your donors are in for the long haul, these things can decimate a development program.

I love my donors. But I don’t count on them to stick around.