you can estimate your income based on your last year's income and/or your current pay. you will need to keep the exchange informed if your income is significantly different than you estimated when you applied for coverage. if your income rises during the year your subsidy may change during the year. any differences between subsidies paid and what you were actually eligible for will be resolved when you pay your income taxes.
how do you determine your income when buying health insurance if next years' income is unpredictable?