When people say a loan is "in underwriting," it sounds like a black box. It isn't. Underwriting is just the process of a lender deciding whether to approve your loan and on what terms — by checking two things: that you can repay it, and that the loan follows the rules of whoever's going to back it.
That second part surprises people: the lender mostly isn't making up the rules. They're applying someone else's rulebook.
Whose rulebook?
Which guidelines apply depends on your loan type:
- Conventional loans follow Fannie Mae and Freddie Mac guidelines.
- FHA loans follow HUD / FHA rules.
- VA loans follow the Department of Veterans Affairs.
- USDA loans follow the USDA.
On top of that, an individual lender can add its own stricter rules — called overlays. So two lenders working from the same Fannie Mae rulebook can still give you different answers, because one layered extra caution on top.
What underwriting is actually checking
Most of it comes down to a few pillars lenders have weighed forever — often called the four C's:
- Credit — your score and your history. Have you paid on time? Any collections, bankruptcies, or foreclosures? Each program sets its own minimums.
- Capacity — can you afford the payment? This is where your debt-to-income ratio (DTI) comes in: your monthly debts measured against your income. Programs cap how high it can go.
- Capital — your assets: the down payment, the closing costs, and often "reserves" (months of payments left over after you close).
- Collateral — the property itself, judged by the appraisal. The home has to be worth the loan and be acceptable security for it.
Some add a fifth, Conditions — the loan's terms and the broader context. The exact thresholds for all of these — minimum scores, maximum DTI, required reserves — vary by program and shift over time, so treat them as moving targets, not fixed lines.
The software, then the human
Most files first run through an automated underwriting system — Fannie Mae's Desktop Underwriter (DU), Freddie Mac's Loan Product Advisor (LPA), or FHA's TOTAL Scorecard. These give an initial read (for example, "approve/eligible" or "refer") from the data entered.
But the software doesn't get the last word. A human underwriter then verifies the documentation behind that data — pay stubs, W-2s, tax returns (especially if you're self-employed), bank statements, employment verification — and issues conditions: the list of items you need to clear. Satisfy them all and you reach clear to close.
Why two lenders can treat you differently
Same income, same credit, two different outcomes — it happens, and it's usually one of two things: a different loan program (different rulebook) or a lender's overlays (stricter house rules). It's a real reason to talk to more than one lender if your file sits anywhere near a guideline edge.
The takeaway
Underwriting isn't a mood; it's a rulebook plus a verification. The rulebook belongs to whoever backs your loan — Fannie, Freddie, FHA, VA, or USDA — and your lender may add overlays on top. What they're checking hasn't changed in decades: your credit, your capacity to repay, your capital, and the collateral. Know which program you're in, and you'll understand most of what underwriting is asking for.
Specific score minimums, DTI limits, and reserve requirements vary by program and lender and change over time. Confirm the current numbers for your loan with your lender.