Per the IRS Partner's Instructions for Schedule K-1
(Form 1065), page 2: Basis Rules
Generally, you may not claim your share of a partnership loss (including a capital loss) to the extent that it is greater than the adjusted basis of your partnership interest at the end of the partnership's tax year. Any losses and deductions not allowed this year because of the basis limit can be carried forward indefinitely and deducted in a later year subject to the basis limit for that year.
The partnership isn't responsible for keeping the information needed to figure the basis of your partnership interest. Although the partnership does provide an analysis of the changes to your capital account in item L of Schedule K-1, that information is based on the partnership's books and records and cannot be used to figure your basis.
You can figure the adjusted basis of your partnership interest by adding items that increase your basis and then subtracting items that decrease your basis.
Use the worksheet on page 2 of these instructions to figure the basis of your interest in the partnership.
For more details on the basis rules, see IRS Publication 541 Partnerships,