Next year I'll start receiving Social Security benefits. They are paid a month in arrears, so that the benefit for December 2019 will actually be paid in January 2020.
If this were salary, that payment for December, made in January, would be 2020 income, not 2019 income. Is it the same for Social Security -- benefits are income in the year when the payment is made available to me, not the year for which it is paid?
(I know I'll find out the answer when I get a Form 1099 early in
2020. But I like to estimate my tax in advance due as closely as possible, so that I can have appropriate amounts withheld since I'm still working.)