Real Estate Calculators

Rental cash flow analyzer

Plug in rent, PITI, vacancy, CapEx reserves, and management — see whether a deal truly cash flows after every real expense, not just the Zillow math.

Analyzer · Real rental cash flow with full expense stack
No signupsInstant resultsPDF exportWritten by investors
Income
Fixed monthly costs
Variable reserves (% of effective gross income)
Real monthly cash flow
-$392
Deal does NOT cash flow with real expenses
Naive 'Zillow math' cash flow
$685
Rent − mortgage only (what most people calculate)
Hidden expense gap
$1,077
Per month of reserves, mgmt, and CapEx missed by simple math
Net operating income (NOI)
$12,694
Annual, before debt service — used for cap rate
Annual debt service
$17,400
P&I × 12
DSCR
0.73x
Below the 1.25x DSCR lenders typically require

Why most 'cash flowing' rental deals don't cash flow

The single most common math error new landlords make is underestimating operating expenses. A property posted as "cash flowing $450/month" by a wholesaler or Zillow rental listing almost always does the math the same way: rent minus mortgage minus a token estimate of taxes and insurance. That's not cash flow. That's an optimistic number that ignores four real costs: vacancy, management, repairs, and capital expenditures.

The analyzer above shows both numbers side by side. The naive "Zillow math" cash flow (rent minus mortgage) and the real cash flow after full operating reserves. The gap between them is where most new landlords lose money.

Real example: $285,000 duplex in Kansas City

Consider a real deal. $285,000 duplex, 25% down ($71,250), $6,200 closing, 7.125% 30-year conventional. Monthly P&I: $1,437. Property tax: $3,540/year ($295/month). Insurance: $1,680/year ($140/month). Rent: $1,350/side = $2,700/month total.

Naive (Zillow) math: $2,700 rent − $1,437 mortgage − $295 tax − $140 insurance = $828/month cash flow. Looks amazing. 14% cash-on-cash return. Let's buy the deal.

Real math with operating reserves:

  • Gross income: $2,700/month × 12 = $32,400
  • Vacancy 8%: −$2,592 = $29,808 effective gross
  • Management 8% of effective gross: −$2,385
  • Repairs 8%: −$2,385
  • CapEx 8%: −$2,385
  • Property tax: −$3,540
  • Insurance: −$1,680
  • NOI = $29,808 − $2,385 − $2,385 − $2,385 − $3,540 − $1,680 =$17,433
  • Annual debt service: $1,437 × 12 = $17,244
  • Annual cash flow: $17,433 − $17,244 = $189/year = $16/month

The deal that looked like $828/month cash flow is actually $16/month cash flow with full reserves. Still positive, but a very different investment than the listing suggested. One bad year (extended vacancy + CapEx hit) puts you underwater.

The four reserve categories, explained

Vacancy (5–10%)

Every rental will be vacant some of the time — tenants move out, units need turn time, leases expire. Even if your current tenant has been there 5 years, you need to budget for the eventual turn. A typical turn takes 2–4 weeks of vacancy plus $1,500–$3,500 in paint/flooring/cleaning. Spread that across the lease term, it's roughly 6–8% of gross rent in a stable market, 10%+ in turnover-heavy areas.

Property management (8–10%)

Even if you self-manage, include the line. Three reasons. First, self-managing is work and you should value your time. Second, including PM makes your returns comparable across deals and across investors. Third, the day you decide to scale past 4–5 doors you'll want a PM, and your deal math needs to still work with that fee included.

Repairs (5–10%)

Not the big CapEx items — those are separate. This is the month-to-month stuff. Leaky faucet: $175. Garbage disposal fail: $300. HVAC service: $125. Lock rekey: $90. These add up to $800– $1,800 per door per year on a typical single-family. Budget 5% on newer properties, 10% on older ones.

CapEx (5–10%)

The big systems with predictable lifespans. Roof: 20–25 years, $10K–$18K replacement. Furnace: 18–22 years, $5K–$8K. Water heater: 10–12 years, $1,500–$2,500. Flooring: 10 years per area. Paint: 5–7 years. Sum the replacement cost, divide by remaining useful life, and that's your monthly CapEx reserve. On a typical rental it's 5–10% of gross rent. Most landlords under-reserve CapEx until year 3 when the water heater dies and they realize they have no reserves. Don't be that landlord.

What 'good' cash flow looks like

On a fully-reserved rental:

  • $0–$100/mo:Break-even deal. Acceptable in appreciating markets if you're playing the long game, risky in flat markets.
  • $100–$250/mo: Reasonable cash-flow deal. Most conservative investors buy here.
  • $250–$450/mo: Strong cash-flow deal in most markets. Rare on the MLS in 2025-2026; usually requires off-market acquisition or a BRRRR.
  • $450+/mo: Exceptional. Either a home-run deal, a BRRRR with high equity, or a small multifamily.

Related tools

Use our cash-on-cash return calculator to see the return on your invested capital. The cap rate calculator benchmarks NOI yield against market comps. Stress-test vacancy assumptions with our rental vacancy impact calculator. For the full rental investment decision, see our investment property calculator.

Frequently asked questions

Why does this tool show so much less cash flow than the Zillow estimate?

Because Zillow-style 'rent minus mortgage' math leaves out every operational reality of a rental. Real rentals have vacancy (tenants move out, units sit empty), management fees or your own time, property management's smaller sibling: repairs (every HVAC tune-up, every leaky faucet), and CapEx reserves for the big systems that fail on a schedule. Add all of those at industry-standard reserve rates and the picture shifts dramatically. On a $2,100/mo rent with $1,450 P&I + $435 escrow (tax/insurance), naive math shows $215/mo cash flow. Real math shows whatever's left after 24-32% of effective gross income goes to vacancy + management + repairs + CapEx — often $40-$120/mo, sometimes negative.

What are the 'right' reserve percentages?

Industry benchmarks that most experienced landlords use: Vacancy 5-10% (higher in B/C class areas, lower in A class). Property management 8-10% of collected rent (if self-managing, keep the line at 8% anyway — it values your time and makes cash flow comparable across deals). Repairs 5-10%, leaning higher on older properties. CapEx 5-10%, leaning higher on properties with old major systems (20+ year roof, 15+ year HVAC). On a 50-year-old property, I run 10%/10%/10%/10% = 40% total. On a newly-built turnkey, 5%/8%/5%/5% = 23%.

Is this tool too conservative?

If you run it on turnkey deals in cash-flow markets, yes — you'll see negative cash flow on some deals that experienced investors happily buy and hold. That's because conservative assumptions protect beginners from deals that LOOK good but don't survive bad years. If you've owned rentals through a 12-month eviction and a $14,000 roof and know how to operate through it, run it at 5%/5%/5%/5% for your own deals. If you're underwriting your first deal, keep the 8%/8%/8%/8% floor. The deal that looks marginal at those reserves will still be fine in year 1. The deal that looks bad at those reserves will kill you in year 3.

What does DSCR mean and why does it matter?

DSCR (Debt Service Coverage Ratio) is NOI divided by annual debt service. A DSCR of 1.0 means the property just barely covers its own mortgage. 1.25x means NOI is 125% of mortgage payments — there's a 25% cushion. DSCR matters for two reasons. First, most rental investment lenders (especially DSCR-specialist lenders like Kiavi, Lima, Finance of America Commercial) require 1.20-1.25x minimum. Below that, you can't refinance even if LTV is good. Second, it's a sanity check on your deal. A DSCR under 1.15x means any bad luck (vacancy, CapEx surprise) puts you underwater on month-to-month operations.

What if my deal doesn't cash flow in this tool?

Three options. First, negotiate the price. If rent is fixed and your target return requires a lower basis, offer less. Many sellers would rather close at a discount than relist. Second, refinance your assumptions — if you're buying in a primary market for appreciation, not cash flow, accept $50-$100/mo cash flow as break-even and bet on year-5-plus returns. Third, walk away. Most deals that don't cash flow at conservative reserves don't cash flow period — they're cheaper than 'lose money in real estate' later.

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