The Bill Saver May 2013 is the cheapest tariff by paying by Receipt of Bill.

GoFix11 is the cheapest, or tends to be when paying by Direct Debit.

The £100 Dual Fuel Direct Debit discount is applied on the 13th month as credit on your account. You don't get it if you change supplier during this time, but if you move home and take Npower to the new property or want to change tariff then you should. There's also no cancellation fee on the Bill Saver May 2013 tariff either.

I'm looking to switch tariff for electricity - does anyone know if the moneysupermarket calculator factors in the £100 annual discount which is part of the Bill Saver May 2013 deal and/or assumes payment by monthly DD when doing the comparison? I couldn't tell .

The tariff is coming up as the cheapest option for me but I wouldnt want to have to be stuck with NPower for 12 months if the major saving came as the annual discount given that prices could be hoiked up during the 12 months which could make the tariff a loser.

Any help gratefully received!!!