The prediction of a forming limit diagram (FLD) for aluminium alloy sheet using finite element analysis without implementing pre-defined geometrical imperfections or material imperfections is studied. The limit strains of the FLD are determined by applying a new proposed localization criterion in the dome stretching test. The elements just outside the necking area, where their major and minor principal strains have no simultaneous change after localized necking happens, are chosen as the reference elements for measurement of limit strains. Simulations are carried out for various strain paths ranging from balanced biaxial stretching to uniaxial stretching. The predicted FLD of AA 5182-O is compared with an experimentally determined FLD and very good agreement is achieved. It is demonstrated that FLDs can be predicted by the finite element method without requiring any assumed geometric or material imperfections in the numerical model.