We discuss the timing of tradeoffs in discrete life history models. Wi
th a simple mathematical example we show that different assumptions ab
out the temporal order of costs and benefits resulting from a reproduc
tive effort can lead to qualitatively different predictions. We examin
e two models taken from the literature, in which an implicit assumptio
n is that benefits from reproductive efforts are received before the c
orresponding costs are paid. We show that the reverse assumptions woul
d have led to very different results. Since there is no biological bas
is for a bias towards a particular set of assumptions, we conclude tha
t a more flexible approach should be used when studying optimality pro
blems that are based on discrete life histories.