Since there is no tax law for “LLC”, the IRS lets you choose how it will be taxed. There are only two tax codes: corporate and individual (S-corp and partnership are provisions within the individual tax codes).
An LLC with only one member can choose between corporate and individual taxation. LLCs with more than one member can choose between partnership and corporate. You can further choose corporate taxation between S- and C-Corp.
Advantages and disadvantages. This is just a general outline; there are many more nuances than I can cover here.
Corporate: generally a lower tax rate than individuals and avoids self employment tax. However, to get cash out of a corporation, it has to declare a dividend or distribution of income, which is taxed again at the personal level (the infamous “double taxation” issue). For this reason it’s not preferred for any investment that spins off cash to the owner.
S-Corp: income is taxed at the higher personal rates of the owner(s), but is NOT subject to self employment taxes IF the corp pays the owner a “reasonable” salary. Distributions from profits are taken tax free. However, this comes at a price: the hassle of dealing with the payroll taxes monthly or quarterly. Passive losses pass through and may be limited.
Both C- and S- Corp: receive some additional benefits such as being able to offer benefit plans to employees, etc. Conversions or exchanges of property or investments may be considered a sale for tax purposes, triggering gain.
Partnership: income is taxed at the higher personal rates of the owners. income may be further subjected to self-employment taxes if the owner is authorized to contract on the LLC’s behalf or works more than 750 hours for the LLC. No further tax on distributions of income. Passive losses pass through and may be limited.
Sole Proprietor or “Disregarded Entity”: so named because the IRS “disregards” the LLC for tax purposes. This has no effect on liability protection; it is only a tax decision. Taxed at the owner’s personal rates. generally subject to self employment taxes. No further tax on distributions. Passive losses may be limited.
I’m sure I’ve left out some things; as I said, there are many other factors (is the member a manager, guaranteed payments, etc. (Dave will let me know where I’ve messed up!)
Changing your tax preference can be done, but there are restrictions: Only once every 5 years and it requires IRS approval. This may have changed.