20 CFR §418.1240

If you know that the information you provided to us about the more recent tax year that we used has changed, you should tell us so that we can determine if your income-related monthly adjustment amount should be eliminated or adjusted. We will accept new modified adjusted gross income information at any time after your request until the end of the calendar year following the more recent tax year(s) that we used. For us to make a new initial determination using your new modified adjusted gross income information, you must provide evidence as described in § 418.1265 to support the reduction or increase in your modified adjusted gross income. If you amend your Federal income tax return for the more recent tax year we used, we will use the rules in § 418.1150.