Is a cash inheritance included in MAGI for calculating Medicare Part B payments?. Will increased payments go back down in future years?

[Texas Roger]

A cash inheritance that is not in a tax deferred account of some type is not taxable and not entered on your tax return. It is therefore not included in the MAGI for calculating Medicare Part B payments. 

If the inheritance was in a tax deferred account and you take a distribution, the amount of the distribution that is taxable would be entered on your tax return and included in the MAGI.

[SweetieJean]

Your income for purposes of increased Medicare premiums is recalculated each year. For example: 2017 premiums are based upon 2015 income; 2018 premiums are based upon 2016 income.
<a rel="nofollow" target="_blank" href="https://www.ssa.gov/pubs/EN-05-10536.pdf">https://www.ssa.gov/pubs/EN-05-10536.pdf</a>