The ADU Income Calculator on this site is built specifically for NYC homeowners who want to understand the real earning potential of adding — or converting — a secondary unit on their property. This guide walks you through how to use it, what the inputs mean, and how to interpret the results to make a smart decision about building an ADU in 2026.
ADUs — also called backyard apartments, in-law suites, garage conversions, or basement rentals — are one of the fastest-growing strategies for Staten Island homeowners who want to generate income without selling their home.
What Is the ADU Income Calculator?
The ADU Income Calculator is a free, interactive tool that estimates: monthly rental income based on ADU type, size, location, and bedroom count; annual net income after factoring in vacancy, property management, and maintenance costs; cash-on-cash return on your construction investment; and 10-year cumulative cash flow to see the long-term earning picture. It’s the tool you use before you call a contractor — to decide whether the numbers actually work for your situation.
Step-by-Step: How to Use the ADU Income Calculator
Step 1: Select Your ADU Type
The calculator offers several ADU configurations common in Staten Island and Brooklyn:
- Basement apartment — The most common ADU conversion on Staten Island. Converting a finished basement to a legal rental typically costs $40,000–$80,000 depending on egress, kitchen, and bathroom requirements.
- Detached backyard unit — A standalone structure in your backyard. NYC’s new pre-approved ADU designs (released early 2026) have significantly reduced design costs for this option.
- Garage conversion — Converting an attached or detached garage to a habitable unit. Popular in Eltingville, New Dorp, and Great Kills.
- Above-garage unit — An addition above an existing garage. Higher construction cost but generates significant rental income.
Step 2: Enter Square Footage and Bedroom Count
The calculator uses your square footage and bedroom count to benchmark against current Staten Island rental market data. A studio under 400 sq ft in Great Kills might rent for $1,400–$1,600/month, while a 2-bedroom legal basement apartment in the same neighborhood can command $1,800–$2,200/month. Be realistic with your inputs — check current listings on StreetEasy or Zillow Rentals to calibrate your estimate.
Step 3: Enter Your Location
The calculator adjusts for location, as rental rates vary significantly across Staten Island. The North Shore (St. George, Stapleton, New Brighton) commands higher rents than the South Shore (Tottenville, Huguenot), largely due to proximity to the Staten Island Ferry for Manhattan commuters.
Step 4: Enter Your Build Cost
Use these general ranges for 2026 in Staten Island and Brooklyn:
- Basement conversion (partial finish): $40,000–$65,000
- Basement conversion (full legal apartment): $65,000–$110,000
- Garage conversion: $50,000–$90,000
- Detached backyard ADU (pre-approved design): $150,000–$280,000
- Detached backyard ADU (custom design): $220,000–$400,000+
If you’re applying for the NYC Plus One ADU Program, you may be eligible for a low-interest or forgivable loan up to $395,000 for construction costs.
Step 5: Set Your Vacancy Rate
A 5% vacancy rate (roughly 3 weeks per year) is a reasonable baseline for well-managed Staten Island ADUs. High-demand areas near the ferry: budget 3%. Self-managing a unit in a less walkable area: budget 8–10%.
Step 6: Interpret Your Results
The calculator returns four key metrics: Monthly Rent (market-calibrated gross rental income estimate), Annual Net Income (after vacancy, management, and maintenance), Cash-on-Cash Return (annual net income divided by out-of-pocket construction cost — a healthy ADU should return 8–15% in Staten Island’s current market), and 10-Year Cash Flow (cumulative net income over a decade). If your cash-on-cash return is 10%+ and you break even in under 8 years, the ADU is a financially strong decision.
Quick Scenarios: What ADUs Actually Return on Staten Island in 2026
Scenario A: Basement Apartment, Great Kills, $75,000 Build
Legal 1-bedroom basement with egress, separate entrance, full kitchen and bath. Monthly rent: ~$1,700. Annual net income: ~$18,700. Cash-on-cash return: ~24.9%. Payback period: ~4 years. ✅ Excellent.
Scenario B: Detached Backyard Unit, New Dorp, $220,000 Build
500 sq ft studio backyard unit using a pre-approved NYC ADU design. Monthly rent: ~$1,600. Annual net: ~$17,200. Cash-on-cash return: ~7.8%. Payback period: ~13 years. Better if funded via the Plus One ADU forgivable loan.
Scenario C: Garage Conversion to 2-Bedroom, Eltingville, $85,000 Build
Detached garage converted to 650 sq ft 2-bedroom unit. Monthly rent: ~$2,000. Annual net: ~$22,100. Cash-on-cash return: ~26%. Payback period: ~3.8 years. ✅ Excellent — verify zoning with NYC DOB before starting.
→ Run your own scenario in the ADU Income Calculator →
NYC ADU Programs That Can Reduce Your Costs
Plus One ADU Program: NYC’s flagship program provides low- or no-interest loans and construction grants up to $395,000. Income eligibility up to 165% of Area Median Income, with priority for homeowners at or below 100% AMI.
Pre-Approved Designs: In early 2026, NYC released 11 pre-approved ADU building designs — eliminating the design approval phase and reducing architectural costs by $10,000–$30,000.
→ Full guide: Can You Build an ADU on Your NYC Property? (2026)
→ Calculate full investment ROI on a multi-unit property →
Ready to Run Your Numbers?
An ADU can transform your home from a pure expense into an income-generating asset. But the zoning, permitting, and financing landscape in NYC is complex. Joseph Ranola works with Staten Island homeowners who are evaluating ADUs both as a personal income strategy and as a value-add before listing.
📞 (347) 446-2573 | 📧 [email protected] | 📅 Schedule a free ADU strategy consultation →
ADU Income Calculator FAQ
Is the ADU Income Calculator free to use?
Yes — completely free, no sign-up required. Access it here.
How accurate are the rental income estimates?
The estimates are benchmarked against current Staten Island rental market data and updated periodically. They represent realistic market rents for well-maintained units — not aspirational top-of-market figures. For a property-specific estimate, contact Joseph directly.
Can I use the ADU calculator for Brooklyn properties?
Yes. While the calculator is calibrated primarily for Staten Island market conditions, you can enter custom rent figures reflecting Brooklyn’s generally higher rental market. Brooklyn ADUs — especially in Bay Ridge, Dyker Heights, and Bensonhurst — often command 15–25% higher rents than comparable Staten Island units.
Does the calculator factor in financing costs?
The current version calculates cash-on-cash return based on net operating income relative to your construction cash investment — it does not model financing costs on the ADU build itself. If you’re financing through a HELOC or home equity loan, subtract your annual debt service from the annual net income to get your true cash-on-cash return.
