Complex indeed! My first thought is to ask what your payslip shows, as this should make quite clear what you are being paid for. If you haven't had it yet, then I think it is too soon to try to work it out. That said, it does sound to me like you've not been paid your full entitlement for the work you've done so far. Are you sure that the money you've received is actually for those three days, and not for earlier work such as KIT days, or the tail end of your maternity entitlement? I'd have expected work so late in the calendar month to have ended up in June's pay packet, since it's very late for PayRoll to be processing things for such soon payment. As for the approximate calculation of your earnings: Firstly, most authorities simply pay the salary over 12 equal monthly instalments. So, for a full working month you would earn 1/12th of your annual salary. Secondly, in such circumstances, your return-to-work date would be the only significant factor for your salary. So, if you started work on Monday 28th May then you'd be entitled to your salary from that date - around 4/31ths of your usual monthly amount (or 4/365ths of your salary) Given that your salary is approximately £37,980, I'd expect your pay for May to be 4/365ths of that amount, so just over £400 before tax. Therefore, it does seem like you've been underpaid, if that's what the payment is for. But as I said to start with, without looking at your payslip, you cannot be clear.