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What is Day 1 Certainty (D1C)?

Day 1 Certainty (D1C) is a Fannie Mae program that allows lenders to use automated verification sources for income, assets, and employment. When lenders use D1C-approved verification sources, they can:
  • Accept verified data without requiring additional documentation
  • Reduce underwriting conditions and borrower tasks
  • Accelerate the loan process
  • Improve borrower experience
  • Achieve rep and warrant relief through AUS (Automated Underwriting System) integration
D1C enables programmatic loan origination with minimal borrower friction by eliminating the need for manual data entry and document uploads when verified data is available from approved sources.

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What is Asset and Income Modeler (AIM)?

Asset and Income Modeler (AIM) is Freddie Mac’s equivalent program to D1C that provides automated verification of income and assets. AIM offers similar benefits:
  • Automated income and asset verification
  • Reduced documentation requirements
  • Faster loan processing
  • Fewer underwriting conditions
  • Rep and warrant relief through AUS integration
Like D1C, AIM enables lenders to accept verified data from approved sources without requiring additional documentation, accelerating loan processing and improving borrower experience.

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Why D1C and AIM matter

D1C and AIM programs are essential for modern mortgage origination because they:

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Reduce documentation requirements

When data comes from D1C/AIM approved sources, lenders can accept verified data without requiring borrowers to upload pay stubs, bank statements, employment letters, or other traditional documentation.

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Accelerate loan processing

Automated verification is faster than manual document review, reducing time to close and improving borrower satisfaction.

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Enable programmatic origination

For programmatic loan origination where manual intervention should be minimized, D1C and AIM approved sources are essential. They allow lenders to verify borrower information automatically without manual review.

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Provide rep and warrant relief

When data is verified through D1C/AIM approved sources and properly integrated with AUS systems, lenders can achieve rep and warrant relief, reducing liability and risk.

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Generate the path of least resistance

Using D1C and AIM approved sources generates the path of least resistance with the least amount of conditions, making loans easier to process and close.

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Coverage and maturity

Both D1C and AIM ecosystems are mature with >90% coverage of banks, payroll providers, and other data sources. This means most borrowers can benefit from automated verification. The D1C and AIM ecosystems cover:
  • Payroll providers: Most major HRIS systems and payroll processors
  • Banks and financial institutions: Coverage of major banks and credit unions
  • Employment verification: Automated employment and income verification services
  • Asset verification: Bank account and asset verification services

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Approved verification sources

D1C and AIM programs maintain lists of approved verification sources. These sources have been vetted by Fannie Mae and Freddie Mac to meet specific data quality and security standards. The following table shows which vendors are D1C/AIM approved for each verification type:
VendorIncome/EmploymentAssets
Truv✅ Approved✅ Approved
Plaid❌ Not approved✅ Approved
The Work Number (TWN)✅ Approved❌ Not available
For the complete and current lists of approved vendors, see:
Pylon only onboards approved sources: Pylon only integrates with vendors and their specific products (SKUs) that are already D1C/AIM approved. You don’t need to verify source approval—Pylon ensures all available integrations meet D1C/AIM requirements.

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How D1C and AIM work

When lenders use D1C/AIM approved verification sources:
  1. Borrower provides minimal information: Instead of uploading documents, borrowers provide basic information (e.g., SSN for income verification, connect bank account for assets).
  2. Automated verification: Lenders pull verified data from approved sources, which are automatically assessed by Fannie Mae and Freddie Mac systems.
  3. Reduced conditions: Since data is pre-verified, underwriting requires fewer conditions and tasks, accelerating the loan process.
  4. Rep and warrant relief: When properly integrated with AUS systems, verified data from D1C/AIM sources enables rep and warrant relief.

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Best practices

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Vendor waterfall strategy

Since not all vendors have coverage for every institution or payroll provider, implementing a vendor waterfall strategy is important to maximize verification success. Different vendors have varying coverage rates, costs, and capabilities—some may have better coverage for certain types of institutions or employers, while others may be more cost-effective. A waterfall approach allows you to:
  • Maximize coverage: Try multiple vendors to increase the likelihood of finding a match for the borrower’s institution or employer
  • Optimize costs: Prioritize lower-cost vendors when multiple options are available. For example, The Work Number is approximately 5x more expensive than other vendors like Truv. Since Pylon covers the cost of unfunded loans in the closed per loan fee, using higher-cost vendors when you have a low application-to-funded loan ratio can result in increased underwriting fees per loan.
  • Improve borrower experience: Reduce the need for borrowers to provide traditional documentation by attempting automated verification first

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General best practices

  • Prioritize automated verification: Always attempt automated verification through D1C/AIM approved sources before requesting traditional documentation
  • Monitor verification status: Poll Pylon’s API regularly. When verifiedAmount or verifiedBalance fields are populated, automated verification was successful and no additional documentation is typically required