ESDU 77012 gives a method for estimating the forward shift of aerodynamic centre by treating the nacelle as an annular wing of diameter equal to the nacelle spanwise width. A graph gives the lift-curve slope for an annular wing as a function of its width to length ratio, the lift is assumed to act at the nacelle lip, and a correction term for the effect of the wing upwash field is added. The method is validated by comparing predictions with wind-tunnel data taken from the literature for both free-flow nacelles and nacelles with variable mass flow and is found to predict the shift to within 0.02 of mean aerodynamic chord. The wing lift-curve slope, also required in the method, is obtained from ESDU 70011 and the aerodynamic centre of the wing-fuselage combination, to which the forward shift is applied, is obtained from ESDU 76015.