Long term care deduction- my itemized deduction doesn't include all the long term care premium.

[CS]

Not all the long term care premium of the taxpayer is carrying over to schedule A. 

What causes some to be presumably disallowed?

[Accountant-Man]

There is an annual maximum that is allowed to be deducted.

[George4Tacks · Accepted solution]

When all else fails, read the instructions. https://www.irs.gov/instructions/i1040sca#idm140545383582080

Limit on long-term care premiums you can deduct.

The amount you can deduct for qualified long-term care insurance contracts (as defined in Pub. 502) depends on the age, at the end of 2018, of the person for whom the premiums were paid. See the following chart for details.

IF the person was, at the end of 2018, age . . .THEN the most you can deduct is . . .

40 or under                                                          $ 420

41–50                                                                  $ 780

51–60                                                                  $ 1,560

61–70                                                                  $ 4,160

71 or older                                                           $ 5,200