Well when I filled out the form and used the calculate button it did give a figure.
I filed this without payment.
But when I contacted the revenue office by phone they gave me a different figure.
Putting 2 and 2 together (I couldn't get back to them as they were using the answering machine ) it seems like the figure she gave was a neat 10% above what I thought it was.
But I need to be certain as time is getting short and if I could see where the late payment rates were laid out I could do my own calculation.
By the way I am talking PRSI-SELF.