The entire amount is includible on your 2019 tax return (Form 1040 line 5a). The taxable amount (line 5b) is determined by knowing only the total amount on the SSA-1099, the amount of the lump-sum for 2018 and certain details of your 2018 tax return. There is no need (and therefore no provision) to separately enter the portion that is your benefits for 2019. The portion that is your 2019 benefits is calculated on the Lump-Sum Sum Social Security Worksheet by simply subtracting the lump-sum amount(s) from the total.