I’m surprised there’s no mention of the rule of pi - take the estimates (guaranteed to be optimistic) and multiply by pi. As reasonable and accurate as just about everything else there. :D

I used to work for a non-profit whose founder's goal was to receive enough in donations/grants to become self-sustaining (for overhead - rent, utilities, office supplies, advertising, etc)

At the time (~20y ago), his aim was 2pi million $$

At an annual draw rate of 5%, it'd provide >$300k year in overhead funding - so that only staff / additional special project funding would need to come from new grants