BACKGROUND We will assess to what extent in vitro fertilization (IVF) is effective in increasing the number of births overall and whether earlier application of IVF will increase this number. METHODS We simulate 100 000 women trying for their first and second child. Natural and IVF pregnancy rates and infertility rates are age-dependent and based on published data. The age at which women start trying for their first child is based on the Netherlands 2002 data. Three cycles of IVF are given during a 12-month period after 1 or 3 years of trying to conceive unsuccessfully. Main outcome measures are live born deliveries and children, both naturally conceived or after IVF, as well as numbers of singletons, twins and triplets, the total fertility rate (TFR) and the number of IVF cycles performed. RESULTS Full access to IVF after 3 years increases the TFR by 0.08 children. Applying IVF after 1 year leads to an additional TFR increase of 0.04, with double the number of IVF cycles and twin and triplet children, and a shift from naturally conceived children to IVF children. CONCLUSIONS Full access to IVF after 3 years is important. It does increase the TFR. Early availability of IVF would further increase the TFR, but with side-effects and high costs.