My understanding is this. It's kind of backasswards.
Your estimated income for 2014 (typically based on your 2012 actual income) will determine a maximum percentage of income that your health insurance will cost. As an example, a 58 yo couple with $60,000 of income would be expected to pay up to 9.5% of their income for health insurance (as would a 58 yo couple with $62,000 of income). The subsidy will be based on any excess of the actual cost of your health insurance (or the actual cost of the silver plan if your chose a richer plan) and 9.5% of your income. This difference will be paid directly to the insurer each month and the insured will be responsible for paying the excess of the premium over the subsidy.
However, assuming they have the same insurance plan, the couple with $60,000 of income would get a higher subsidy that they couple with $62,000 of income because the subsidy is based on the excess of the premium over 9.5% of income.
In the process of doing this I noticed that the
Berkeley calculator has been changed and is more refined with respect to the members of the family unit. For our hypothetical couples, each would have gross premium of $1,468 a month.
The couple with $60,000 of income would get a $993 subsidy ($993 = $1,468 - $60,000/12*9.5%) and would pay the insurer $475 a month (9.5% of their income).
The couple with $62,000 of income would get a $977 subsidy ($977 = $1,468 - $62,000/12*9.5%) and would pay the insurer $491 a month (9.5% of their income).
So while subsidies vary with income, the cost of the policy selected by the applicant also comes into play. In the examples above, if these couples picked a cheaper plan that had a premium of $1,000 a month, their subsidies would decline to $525 a month for the couple with $60,000 of income and $509 per month for the couple with $62,000 of income but in each case their net cost would be 9.5% of their income.
Same thing if they are younger so the premium is lower - given the same levels of income the subsidies would be lower because of the lower premium but the net cost of health insurance will be the same if their income is the same.