I am trying to work out a detailed budget for my maternity leave in order to plan how long I will be able to take. I know that SMP is £136 a week, however, I can't find a way of working out how much that will be net after tax, NI and pension contributions. This is my second pregnancy but I can't remember what it worked out as last time! The baby is due at the end of April so my maternity leave will start at the start of the new tax year, if that makes any difference!