look at line 11 of your 1040. that's your AGI for the year. under some circumstances, it is possible for your AGI for a period to exceed the AGI for the whole year. you are not allowed to prorate the annual AGI to get the AGI for the 3,5, and 8 months. the IRS requires you actually calculate what it is. it will not be pro-rata if your income was received unevenly throughout the year. for example, some taxpayers have large capital gains throughout the year. then they take losses in the 4th period to reduce their tax burden. dividends are usually unequal and then there is the issue of the qualified dividend amount for each period. schedule C income would also likely be uneven.
