Seem to have had the same conversation a few times recently where someone has suddenly realised that when SMP stops, they will have to return to work when they had originally planned to take the full year off as 'they wont have enough money coming in'.
To me, it just seems sensible to add up the total amount you will receive in maternity pay and divide it equally between however many months you plan to take off and just spend that.
I just don't understand how, if you don't do this, you imagined that you would get by if you already know you cannot do it on 1 wage? Maternity pay is usually front loaded and so surely its a no-brainer to put some aside for the months you receive 0 pay.