From the 2011 Census round, the population “usual residents” is defined as those who have lived or intend to live for a period of more than 12 months in their place of usual residence. Most of the register-based statistics describe the total number of registered persons in e.g. a population register at a particular moment or period. To estimate the non-registered population of usual residents, capture – recapture methods are available. By making a three list estimation, making restrictions to one day for the period-based registers and a short period for the event-based register, applying a stringent linkage method and deletion of erroneous records, most of the assumptions of the capture – recapture method are met. However, to estimate the number of usual residents, we need to divide the estimated total number of persons into those who stay longer than a year in The Netherlands and those who did not. In this paper we present a method to estimate the number of usual residents even though the residence duration is observed in only one of the lists. We apply the method to Dutch empirical data.