Decreasing fertility has been accompanied with the rising age of mothers almost in all the Western countries. Because of the lack of individual level surveys, the reasons for the postponement are often studied indirectly with the macro level data. Our aim is to explore the individual reasons of the postponement of births with a direct measurement instrument. The postponement of birth is defined as a situation when a person would like to have a child but it will be delayed at least for two years. Three prevailing types of reasons – resources, life stage, partner-related – are analysed in Estonia and Finland. The data from the surveys in 1999 and 2002 are used for analyses. It was found that the life stage and the resource reasons were equally prevailing in both countries among the reasons of postponement of births. However, life stage reasons were statistically more important in Finland than in Estonia. For different age groups and by different socio-demographic variables the reasons of the postponement of births vary considerably.