I used the retrospective method and I'm not sure where I'm wrong 4000/a(12)_5 = 945.61 pa Balance remaining after 3rd payment = 4000(1.07^3)-945.61(a(12)_3 Where a(12)_3= (1-v^3)/i^12= 2.707442889 > Balance = £2339.99 compared to £1763.84 using prospective method