It is correct that these amounts differ. BeFrank gives you an indication based on the assumption that you will continue to work for your current employer until you reach retirement age. You will in that case accrue a constant pension on the basis of your present salary. Mijnpensioenoverzicht.nl is based on the current value you have accrued. It is based on the assumption that you will purchase a pension with the current value, without further accrual.