mcare_pta_premium_share = if(year < 2012, 0, if(agi <= mcare_pta_thresh1(year), mcare_pta_base(year), if(agi <= mcare_pta_thresh2(year), mcare_pta_bracket2(year), if(agi <= mcare_pta_thresh3(year), mcare_pta_bracket3(year), if(agi <= mcare_pta_thresh4(year), mcare_pta_bracket4(year), mcare_pta_bracket5(year)) ) ) ) )