How to Underwrite Commercial Real Estate Deals (Step-by-Step Guide)

By Rainmakers OS · April 2026 · 8 min read

What is CRE Underwriting?

Underwriting a commercial real estate deal means analyzing the financial performance of a property to determine if it's a good investment. You're answering one question: will this property generate enough income to justify the purchase price and cover the debt?

The process involves reviewing rent rolls, profit & loss statements (P&Ls), operating expense reports, and calculating key metrics like NOI, cap rate, DSCR, and cash-on-cash return.

Traditional underwriting takes 4-8 hours per deal. With AI tools like Rainmakers OS, this can be reduced to under 45 minutes.

Step 1: Gather the Financial Documents

Before you can underwrite a deal, you need these documents from the seller or broker:

• Rent Roll — Shows every unit, tenant name, lease terms, monthly rent, and vacancy status
• Trailing 12-Month P&L (T12) — Actual income and expenses for the past 12 months
• Operating Expense Report — Detailed breakdown of property expenses (taxes, insurance, maintenance, management fees, utilities)
• Lease Abstracts — Key terms from each lease (for commercial tenants)

If the seller won't provide these, it's a red flag. Walk away or proceed with extreme caution.

Step 2: Calculate Net Operating Income (NOI)

NOI is the most important number in CRE. It tells you how much money the property generates after operating expenses but before debt service.

Example:

• Gross Potential Revenue: $500,000/year (all units at market rent)
• Vacancy Loss (5%): -$25,000
• Effective Gross Income: $475,000
• Operating Expenses: -$190,000 (38% expense ratio)
• NOI: $285,000

Key check: Compare the seller's stated NOI to your independently calculated NOI. If there's a big gap, the seller may be understating expenses or overstating rents.

Step 3: Determine the Cap Rate

The capitalization rate tells you the rate of return on the property as if you paid all cash (no financing).

Example:

NOI of $285,000 on a $4,500,000 purchase price = 6.3% cap rate

What's a good cap rate?

• Class A (prime locations, new buildings): 4-5%
• Class B (good locations, older buildings): 5-7%
• Class C (secondary markets, value-add): 7-10%
• Class D (distressed, high-risk): 10%+

Cap rates vary significantly by market, property type, and risk profile. Always compare to recent comparable sales in your market.

Step 4: Analyze Debt Service Coverage (DSCR)

DSCR tells lenders (and you) whether the property generates enough income to cover the mortgage payments.

Example:

NOI of $285,000 with annual debt service of $220,000 = DSCR of 1.30x

• Below 1.0x: The property doesn't cover its debt — you'd need to bring cash every month
• 1.0x – 1.2x: Razor thin margins — one vacancy could push you underwater
• 1.2x – 1.4x: Healthy range — most lenders require minimum 1.20-1.25x
• 1.4x+: Strong coverage — comfortable cushion for unexpected expenses

Step 5: Calculate Cash-on-Cash Return

Cash-on-cash measures the return on the actual cash you invested (your down payment + closing costs), not the total purchase price.

Example:

• NOI: $285,000
• Annual Debt Service: -$220,000
• Annual Cash Flow: $65,000
• Down Payment + Closing Costs: $1,200,000
• Cash-on-Cash Return: 5.4%

Target 8-12% cash-on-cash for value-add deals. Stabilized properties may return 5-8%.

Step 6: Stress Test Your Assumptions

Good underwriting isn't just about the numbers — it's about asking "what if things go wrong?"

• What if vacancy jumps to 15%? Does the deal still cash flow?
• What if interest rates rise 1% at refi?
• What if expenses increase 10%?
• What's the break-even occupancy?

If break-even occupancy is above 85%, the deal has thin margins. Below 75% gives you a comfortable cushion.

Using AI to Underwrite Faster

The underwriting steps above traditionally take 4-8 hours per deal when done manually in Excel. With AI-powered tools, you can cut this to under 45 minutes.

Rainmakers OS automates the most time-consuming parts:

• Rent roll parsing: Upload a PDF or Excel rent roll — AI extracts every unit, tenant, rent amount, and lease term automatically
• P&L analysis: Drop in a T12 and get instant NOI, expense ratios, and revenue breakdowns
• Automated calculations: Cap rate, DSCR, cash-on-cash, and IRR calculated instantly
• Risk flagging: AI identifies anomalies — above-market rents, unusual expenses, below-market occupancy

This means you can screen 5-10x more deals per week, giving you a significant edge in competitive markets.

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