Depends on your scheme of service and whether you are on timescale or superscale... For timescale officers, it is dependent on your performance grade too... I know some scheme of service have fixed absolute amount (while some have fixed % of their pay) for all officers with the same performance grade. its very easy to tell actually... just calculate what's your MI increment % over your last drawn gross... if the % has 2 or more decimal points, it is not based on a fixed percentage.