With today´s power uprates in BWR reactors the bundle lift force has become aproblem. The lift force is calculated using a best estimate approach and the resultfrom the calculation should pass the existing lift force margin. Lift force margin isdefined so that the lift force may not exceed 80 % of the fuel weight. The margin issupposed to cover all the uncertainties that exist in the lift force calculations.However, no uncertainty analysis has been conducted to quantify the uncertainties. In this report the uncertainties in the lift force model have been quantified. Each inputparameter to the lift force model which has been assumed to have an uncertainty isassigned a probability distribution. Through the Monte Carlo method and Wilk´smethod an uncertainty propagation has been performed at different points in thereactor´s power flow map. By using these two methods, uncertainty in input datahave been translated into uncertainty in output data. This study has investigated fuelfrom different companies. From the Monte Carlo and Wilk´s method the lift force hasbeen calculated at various probabilities. By using these results, a lift force margin hasbeen calculated for each fuel type and at various probabilities. The results from the uncertainty propagation shows that the current lift force margincorresponds to approximately 95 % probability that lift doesn´t occur for all fueltypes. By using the uncertainty propagation, a new way of calculation the lift forcemargin has been developed.