You'll need to provide or retain documents that verify your eligible cash compensation and non-cash benefit payments during the covered period, including:

Bank account statements or third-party payroll service provider reports documenting the amount of cash compensation paid to employees.

Tax forms (or equivalent third-party payroll service provider reports) for the periods that overlap with the covered period (or alternative payroll covered period):

• Payroll tax filings reported, or that will be reported, to the IRS (typically, Form 941); and
• State quarterly business and individual employee wage reporting and unemployment insurance tax filings reported, or that will be reported, to the relevant state.

Payment receipts, cancelled checks, or account statements documenting the amount of any employer contributions to employee health insurance and retirement plans

Note: If you qualify for the Form 3508S or 3508EZ application, you may not need to gather the FTE documents.
For Form 3508, you'll need to provide documents showing:

• the average number of FTE employees on payroll per week employed by the Borrower between February 15, 2019 and June 30, 2019;
• the average number of FTE employees on payroll per week employed by the Borrower between January 1, 2020 and February 29, 2020; or
• in the case of a seasonal employer, the average number of FTE employees on payroll per week employed by the Borrower between February 15, 2019 and June 30, 2019; between January 1, 2020 and February 29, 2020; or any consecutive 12-week period between February 15, 2019 and February 15, 2020.

You'll need to provide Average FTE for this date range when you apply for forgiveness, but your document(s) can cover periods longer than your chosen reference period. These include:

• Payroll tax filings reported, or that will be reported, to the IRS (typically, Form 941), and
• State quarterly business and individual employee wage reporting and unemployment insurance tax filings reported, or that will be reported, to the relevant state.

If you were unable to return to the previous FTE levels, be prepared to maintain documentation related to any permitted "safe harbor" FTE reduction situations, that include:

• There was an inability to rehire individuals who were employees on February 15 (for example an employee refused a written offer of rehire because they left the area or were concerned about their health status);
• There was an inability to hire similarly qualified employees for unfilled positions on or before December 31, 2020 (for example, you placed advertisements that required certain education or work history, and no applicants applied who met that minimum criteria), or;
• You were unable to return to prior FTE levels because your business was not able to operate at the same level of business activity due to compliance with legal requirements established or guidance related to the maintenance of standards for sanitation, social distancing, or any other worker or customer safety requirement related to COVID-19 (for example local authorities only permitted your restaurant to provide take-out or delivery, or only allowed 50% of the tables to be occupied).
• Your satisfaction of FTE "safe harbor" #2 of Form 3508

Non-payroll documentation is needed to verify the existence of your non-payroll obligations and/or services prior to February 15, 2020 and, for all categories, the eligible payments from the covered period. You may need to retain and/or submit documents including copies of invoices, purchase orders, contracts, cancelled check, etc., for the following:

• Mortgage interest
• Rent or lease payments
• Utility payments 
• Eligible operations and supplier payments
• Property damage and vandalism or looting due to public disturbances that occurred during 2020 not covered by insurance or other compensation
• Worker protection costs to comply with applicable COVID-19 guidance

This list applies to the majority of businesses, but your situation may be unique, especially if you are a self-employed.