ACA 8.5% - partial year coverage ?

[retire48in2018]

If you move to ACA in April, making $87k per year using COBRA Jan-Mar - and monthly premium is above 8.5% -

Is the 8.5% of income for whole year, or 8.5% for April - Dec - 75% of income (9 of 12 months)?

[SecondCor521]

ACA income and subsidies are always done on a tax year basis, so it would be 8.5% of the whole year.

And it's AGI, not income. (Technically it's PPACA MAGI.)

[retire48in2018]

Thanks!

I understand the MAGI (somewhat) from perusing information.