The overall stability of masonry buildings is often provided by unreinforced masonry (URM) shear walls. In the evalution of the loadbearing capacity of these shear walls in-plane and out-of-plane second order effects should be taken into account. In literature and standards limited information for the calculation of the in-plane second order effect of URM shear walls has been introduced. In the informative Annex B of the current version of Eurocode 6, a method for the calculation of the second order effect of masonry shear walls is adopted. This method is based on provisions for reinforced concrete according to the former Dutch concrete standard. In the draft version of FprEN1996-1-1 (2021), an alternative method for the calculation of the second order effect has been introduced. The validity of these two methods for unreinforced masonry shear walls has not been checked yet. In order to get more insight in the behaviour of in-plane loaded unreinforced shear walls, the loadbearing capacity has been determined numerically taking into account second order effects. The results of this calculation have been represented in a design chart, which enables to determine the second order effect for unreinforced rectangular masonry shear walls in a simple manner. It may be concluded that the design methods according to Eurocode 6 are quite conservative and that in most practical cases, the second order effect is relative small for rectangular shear walls in unreinforced masonry.