I am involved in a startup that is discussing whether to form a C Corporation or an LLC. I have some experience with a capitalization table (cap table) but I don't know how to track member equity interest in LLC.
Keeping track of member interests (equity) in a LLC is typically fairly simple. Essentially, you track each member's contributions and distributions (or draws) and apportion retained earnings based on the profit share per member as determined by the LLC operating agreement.
For example, Member 1 contributes $100,000 and Member 2 contributes $100,000 at company formation. The LLC operating agreement states that profits and losses will be apportioned based on the member's contribution as a percentage of total contributed capital - in this case, each member has contributed 50% of total capital. The LLC earns $100,000 net income in its first year, and each member draws $25,000 to cover their personal tax liability. As a result, Member 1 and Member 2 each end the year with $125,000 member interest (a total of $250,000 member interest or equity in the LLC at year end). The equivalent of a cap table for the LLC would simply show the profit/loss share percentage for each member as agreed upon in the LLC operating agreement (you don't really find cap tables for LLCs because there are typically not shares, options and related prices to keep track of since many investors can't or won't invest in an LLC).
Unlike a C Corp, there is no common stock, additional paid-in-capital, or dividends to track from an accounting perspective. And as mentioned above, there is really nothing to manage as far as a cap table because LLC is not the typical vehicle used when your objective is to raise equity capital from outside investors (largely due to the fact that all investors in an LLC are members that are subject to pass-through tax liability).