This package estimates the effective sizes from actual to ancestral time with a coalescent approach. It works on steps of constant size to resolve the probabilities by an approximation of maximum likelihood from a Bayesian posterior distribution. This package works with R software version 3.0.2 or later for VAREFF version 1.1 and R software version 2.10.0 or later for VAREFF version 1.0. This new version contains a new function TMRCA to estimate the time of the detected bottleneck.