How to Underwrite a Philadelphia Duplex the Right Way
Short Answer
>- A Philadelphia duplex underwrite starts with market rents (not in-place rents), applies a 40–50% expense ratio to gross income, and tests the result against your actual debt service at current rates. If the numbers don't work at today's rates, they don't work.
Why seller-provided numbers are almost always wrong
If you want a side-by-side perspective, read What Makes a Philadelphia Duplex a Good Value-Add Deal before finalizing your plan.
When a duplex is listed for sale in Philadelphia, the offering materials typically include "current rents" and sometimes a pro-forma income statement. Both are optimistic. Sellers select the numbers that support their asking price, not the numbers that accurately reflect what you'll actually net.
Start your underwrite from scratch. Use market rents — what a vacant unit at this address, in this condition, would realistically lease for today — not whatever the current tenant pays.
Step 1: Establish gross scheduled income (GSI)
To connect this strategy to execution, review Point Breeze vs Graduate Hospital for a Long-Term Philadelphia Hold, then map your next steps through Philadelphia real-estate investment service strategy and the Philadelphia neighborhood market guides.
Find two to four recently leased comparable units within a tight radius. Same bedroom count, similar finish level. That comp set gives you your market rent. Multiply by 12 and by the number of units.
For a Philadelphia duplex with two 2-bedroom units at $1,600/month each, GSI = $38,400/year.
Step 2: Apply a realistic vacancy allowance
Philadelphia vacancy for stabilized residential properties has historically run 5–8%. Use 8% unless you have a specific reason for confidence (long-term tenants with strong track records). That takes $38,400 down to ~$35,300 effective gross income (EGI).
Step 3: Run actual expenses — not a pro-forma
The 40–50% expense ratio rule exists because sellers and buyers consistently underestimate costs. For a Philadelphia duplex, realistic operating expenses include:
- Property taxes: Pull the actual assessed value and apply Philadelphia's current rate. Do not use the seller's payment — that may reflect an abatement that is expiring.
- Insurance: Budget $1,500–$2,500 annually for a two-unit residential property.
- Maintenance and repairs: $1,200–$2,000/unit/year for a well-maintained older property. More if the systems are aging.
- Property management: 8–10% of collected rent if you're not self-managing. Build it in even if you plan to manage yourself — it reflects the real cost of ownership.
- Capital reserves: $100–$150/unit/month. Flat roofs, plumbing, HVAC, and electric don't break on your schedule.
Applying a 45% expense ratio to $35,300 EGI leaves you with approximately $19,400 net operating income (NOI).
Step 4: Test against current debt service
At a 7.25% rate on a 30-year conventional loan, every $100,000 borrowed costs ~$682/month in debt service, or ~$8,185/year.
If you're buying that duplex for $320,000 with 25% down ($80,000), you're financing $240,000. Annual debt service: ~$19,640.
NOI of $19,400 against debt service of $19,640 = a debt coverage ratio (DSCR) of 0.99. That barely fails the 1.25x DSCR threshold most lenders require.
This is how many Philadelphia duplex deals look right now at asking price. The deal doesn't work — or works very thinly — unless you buy below asking, negotiate favorable terms, or find stronger in-place rents than market suggests.
What to do with this information
If the underwrite produces a DSCR below 1.25 at full ask, the deal needs to come to you at a different price, or you need to have a clear path to increasing rents. Build your offer around the number that makes the deal work, not around what the seller wants.
Internal Links
Related Guides
- What Makes a Philadelphia Duplex a Good Value-Add Deal
- Point Breeze vs Graduate Hospital for a Long-Term Philadelphia Hold
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Related Services and Locations
- Philadelphia real estate investor advisory services
- Invest in Philadelphia real estate with local guidance
- Philadelphia neighborhood market guides
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