Abstract Direct observation of 387 embryos in the early stages of development was combined with observations on breeding behaviour and reproductive biology obtained from the published literature, to estimate the timing of births, oestrus, ovulation and implantation, and to derive estimates of the duration of pregnancy, embryonic diapause and active gestation for crabeater seals (Lobodon carcinophagus). The total duration of pregnancy (conception to birth) is estimated to be 11.3 months (344 days). It is estimated that the pupping season extends from late September to early November, with peak births in mid-October. The estimated mean duration of lactation is approximately 17 days; the mean date of weaning is 31 October (14 October to 17 November); and the mean date of conception is 4 November (18 October to 21 November). Oestrus, ovulation and conception occur approximately 4 days after weaning. Estimates of times of weaning and conception were made assuming that the preimplantation period is the same in all individuals. The mean date of implantation of the embryo is 24 January+/-17 days; the duration of embryonic diapause is 2.7 months (81 days); and the duration of active gestation (implantation to parturition) is 8.8 months (264 days).