How to Use These Popular Investor Formulas
By Marjorie Pellegrini, Broker/Owner – Go North Realty
If you’ve spent more than ten minutes in a real estate investing forum, you’ve heard the buzzwords:
🔸 “It hits the 1% Rule!”
🔸 “I ran the 50% Rule—it pencils out.”
🔸 “The 70% Rule says we’ve got room for profit.”
These rules are everywhere. And they’re great—for fast filters.
Here’s the problem: they’re shortcuts, not strategies. If you follow them blindly, they can lead to bad buys, missed deals, or worse—major ROI miscalculations.
In this article, we’ll break down:
- What each rule means
- When it actually works in today’s market
- What it leaves out
- Real-life examples that test all three
- When to toss the rulebook and do a deep dive
Ready to level up from rule-following to rule-understanding? Let’s get into it.
What Is the 1% Rule?
📌 Formula:
Monthly Rent ≥ 1% of Purchase Price
If a property costs $250,000, it should rent for at least $2,500/month to “meet the rule.”
💡 This is used as a quick screen for potential cash flow.
Pros:
✅ Fast deal filter
✅ Easy to apply
✅ Helps identify high-rent, low-price markets
Cons:
❌ Ignores expenses, financing, or condition
❌ Doesn’t work well in high-cost markets
❌ A 1% deal can still lose money if expenses are high
What Is the 50% Rule?
📌 Formula:
Operating Expenses ≈ 50% of Gross Rent
If rent is $2,000/month, estimate $1,000/month in expenses—before paying your mortgage.
Pros:
✅ Quick cash flow estimate
✅ Useful when doing initial numbers without full details
✅ Helps weed out unrealistic expectations
Cons:
❌ Expenses can range from 30% to 60% or more
❌ Doesn’t apply to new builds, condos with HOA, or furnished rentals
❌ Can give a false sense of security
🛠️ Better to use when comparing similar property types (e.g., duplex vs. duplex).
What Is the 70% Rule?
📌 Formula (for flippers):
Max Purchase Price = 70% of ARV – Repair Costs
ARV = After Repair Value.
Example:
- ARV = $300,000
- Repairs = $40,000
- Max Offer = $300K x 70% = $210K – $40K = $170,000
Pros:
✅ Helps ensure margin for profit
✅ Protects flippers from thin deals
✅ Widely used by wholesalers
Cons:
❌ Based on outdated margins in some markets
❌ Doesn’t account for holding costs, closing fees, or commissions
❌ Assumes perfect resale timing
💡 Many experienced investors now adjust to 75–80% Rule in hot or low-inventory markets.
Real-Life Examples – Do the Rules Hold Up?
🔹 Property A: Turnkey Rental
- Purchase Price: $225,000
- Rent: $2,100/month
- Expenses: $800/month
- Mortgage: $1,000/month
- Cash Flow: $300/month
🧮 1% Rule? Almost! 0.93%
🧮 50% Rule? Nope! Expenses only 38% of rent
✅ But still pencils with positive cash flow.
Verdict: Rules say “maybe,” but real numbers say “yes.”
🔹 Property B: Fix-and-Flip Opportunity
- ARV: $400,000
- Estimated Repairs: $60,000
- Asking Price: $285,000
- Target Margin: $30K minimum
🧮 70% Rule Max Price: $400K x 0.70 = $280K – $60K = $220K
❌ Asking $285K = 16% too high
But… the market is hot. Renovations are minimal. Holding time is short. After costs, projected profit = $25K.
Verdict: 70% Rule says no—but investor with tight ops may say yes.
🔹 Property C: High-Cost Market Condo
- Price: $350,000
- Rent: $2,000/month
- Expenses: $1,200 (incl. $400 HOA)
- Mortgage: $1,400
- Cash Flow: –$600/month
🧮 1% Rule? Nope! Only 0.57%
🧮 50% Rule? Closer to 60%
🧮 70% Rule? Not relevant (not a flip)
Verdict: Every rule fails—and so does the deal. 🚫
So… Which Rule Actually Works in 2025?
The truth? None of them—on their own.
These rules are best used as:
✅ Initial screening tools
✅ Fast math for busy investors
✅ Red flags when a deal looks too good
But once a property passes the sniff test, you must dive deeper:
- Run full cash flow analysis
- Include real-world expense estimates
- Look at loan terms, taxes, insurance
- Know your exit strategy
Don’t let a property pass just because it hits the 1% Rule.
Don’t reject a winner just because it misses the 70% mark.
When to Trust the Rules—and When to Ignore Them
Trust them when:
- You’re reviewing 10+ deals quickly
- You’re investing in stable, predictable markets
- You’re comparing similar property types
- You’re just getting started and need simplicity
Ignore them when:
- You’re buying in high-cost, high-appreciation markets
- You’re house hacking or short-term renting
- You’re financing creatively (seller finance, HELOC, etc.)
- The property has hidden potential (ADU, zoning upsize, etc.)
📣 Rules don’t replace thinking. They help you ask better questions.
Smart Investor Tips to Go Beyond the Rules
🧮 Always build a full pro forma spreadsheet
📉 Stress test your deal at 10% vacancy or 10% rent drop
📊 Track your own market-specific rules
👥 Network with local investors—see what they’re using successfully
📍 Consider location-driven exceptions (e.g., waterfront, downtown, seasonal demand)
🎯 Real investing isn’t about hitting rules—it’s about hitting goals.
WRAP-UP:
The 1%, 50%, and 70% rules are like compass points—they help you navigate. But they won’t drive the car.
Use them as a starting line, not a finish line.
The best investors know when to follow the rules, when to bend them—and when to break them because they ran the real numbers.
📊 Want help analyzing a deal that almost fits—but not quite? Let’s pencil it out together.
Schedule your free ROI review with me at https://calendly.com/gonorthrealty/roi-review-with-marjorie.
Next up in the series:
Cap Rate vs. Cash-on-Cash Return: Know the Difference or Risk Losing Thousands