What form for Self Employed Payments when 90% income earned in one quarter

Hey @vbing5! Great question. Quarterly taxes for self-employed individuals (those who are filing as Sole Proprietors) are 4 equal payments of what you'd owe for the entire year. Whether you make all your income in one quarter, or if it's evenly distributed across all four quarters, you're expected to estimate your total annual taxes owed and make payments every quarter.

If you haven't made prior quarters' payments yet, you may be subject to a (typically small) penalty. Here's an IRS article that you can read up for more info if you haven't seen it yet - Self-Employed Estimated Taxes

I like these two TurboTax articles, too - 

A Guide to Paying Quarterly Taxes

What is the IRS Form 1040-ES Estimated Tax for Individuals?

Also, you may want to check out QuickBooks Self-Employed to help estimate and pay quarterly estimated taxes, and it also keeps all of your business income, expenses, and deductions organized. I like it because it's easy to use and there's the option to bundle with TurboTax so you can send your self-employed tax info to TurboTax through the "export" feature come time to file annual taxes. 

If you don't already have an EFTPS (Electronic Federal Tax Payment System) account setup, you'll need to enroll to make your online payments if this is the way you'd prefer to pay your taxes. If you're a sole proprietor, you'll need to register/enroll as an individual, not as a business with an EIN. Why? Quarterly (Self-Employed) Taxes cover only your Social Security and Medicare taxes. As described in this IRS article, "It is similar to the Social Security and Medicare taxes withheld from the pay of most wage earners." An employer would typically file your personal portion of the Social Security and Medicare taxes, but as a self-employed/sole proprietor, you'd file this through EFTPS as an individual under your Social. 

I hope this helps! :)