Personal Tax - NIC contributions question

It's to do with the weekly threshold for NI. You pay £0 NI on the first £183 a week 12% up to £962 a week.

So the NI on the bonus in the last week is:
(£183 - £0)*0*1 (number of weeks applied)
(£962-£183) * 12% * 1 =93.48
(£10250-£962) * 2 * 1 = 185.76

The income for the other weeks doesn't reach this threshold so only goes up to the £250 that is received