Home›Articles›Guide›The Landlord's Numbers
GUIDE

The Landlord's Numbers: From Cap Rate to Water Bill

From cap rate and depreciation to property tax and plumbing volume — the full calculator stack for evaluating and running a rental property.

Updated 2026-07-07

Free calculators used in this guide

Cap Rate CalculatorRental Property ROI CalculatorDepreciation CalculatorProperty Tax CalculatorTank Volume CalculatorPipe Volume Calculator

Overview

Evaluating a rental property properly means running numbers across domains that don't normally share a spreadsheet: investment return metrics (cap rate, ROI), tax mechanics (depreciation, property tax), and physical building maintenance (plumbing and water system capacity). Most first-time landlords focus entirely on the investment numbers and treat maintenance as an afterthought — until an undersized water heater in a multi-unit building turns into a maintenance call that eats a chunk of that year's return.

This guide walks through both halves: the financial screening and ownership math every landlord needs, and the physical-infrastructure due diligence that determines whether your maintenance costs stay predictable or become a recurring surprise.

Step 1: Screen properties with cap rate

Cap rate — net operating income divided by property value — is the fastest way to compare potential rental properties as unleveraged assets, independent of how you plan to finance the purchase. The Cap Rate Calculator turns your estimated rental income and operating expenses into a single percentage useful for an apples-to-apples comparison across candidate properties in the same market.

Cap rate varies enormously by market — 4-6% in expensive coastal areas driven by appreciation potential, 8-10%+ in lower-cost markets driven by cash flow — so use it to compare within a market, not against a single universal number.

Step 2: Get your real return with financing factored in

Cap rate deliberately ignores financing, which means it doesn't tell you your actual return on the cash you're putting into the deal. The Rental Property ROI Calculator factors in your specific down payment, mortgage terms, and financing costs to calculate cash-on-cash return — the number that actually reflects your investment performance given how you're financing the purchase.

A property with a mediocre cap rate can still be a genuinely strong investment for a leveraged buyer with favorable financing terms, which is exactly why both numbers matter for different questions — cap rate for comparing assets, ROI for comparing your actual investment performance.

Step 3: Factor in the tax mechanics — both ways

Rental property ownership comes with a real, often underused tax benefit: depreciation. The IRS allows landlords to deduct a portion of the property's value (excluding land) annually over a 27.5-year schedule, reducing taxable rental income without any actual cash outlay in that year. The Depreciation Calculator estimates this annual deduction, which meaningfully improves your after-tax return beyond what cap rate or ROI alone show.

The tradeoff: depreciation recapture means the IRS taxes this benefit back (typically up to 25%) when you eventually sell, so the deduction is partly a tax deferral rather than a permanent tax elimination — factor this into your long-term hold-versus-sell planning, not just your annual cash flow.

Property tax is the other tax-side number that's easy to underestimate using a national average. The Property Tax Calculator applied to the specific property's assessed value and local rate often reveals a different number than a seller's historical tax bill, especially since many jurisdictions reassess value at the new purchase price — a common first-year surprise for new landlords.

Step 4: Don't skip the physical infrastructure

Financial due diligence is only half the picture for multi-unit properties with shared water infrastructure — an undersized or aging hot water tank or supply line is a common, predictable source of tenant complaints and maintenance calls that a purely financial analysis misses entirely.

The Tank Volume Calculator and Pipe Volume Calculator help estimate whether existing water infrastructure is adequately sized for current occupancy — buildings often have more units or higher usage today than when original systems were installed. Identifying an undersized shared tank during due diligence, rather than after tenants start complaining, lets you factor a proactive replacement into your maintenance reserve rather than reacting to an emergency failure later.

Key Terms

  • Cap Rate — net operating income divided by property value; a measure of return independent of financing, useful for comparing properties
  • Depreciation — the tax deduction for a property's value (excluding land) spread over a 27.5-year schedule for residential rentals
  • Property Tax — a recurring local tax based on assessed property value, which can change significantly after a sale-triggered reassessment

Frequently Asked Questions

It varies significantly by market — cap rates in the 4-6% range are common in expensive coastal markets with strong appreciation potential, while 8-10%+ is more typical in lower-cost markets where cash flow, not appreciation, is the primary return driver. Use the [Cap Rate Calculator](/cap-rate-calculator/) to compare properties within the same market rather than against a single universal benchmark, since cap rate is most useful as a relative comparison tool.
Cap rate ignores financing entirely — it measures the property's return as if bought with all cash — while the [Rental Property ROI Calculator](/rental-property-roi-calculator/) accounts for your actual mortgage payment, down payment, and financing costs to show your real cash-on-cash return. A property with a mediocre cap rate can still be a strong investment for a leveraged buyer if financing terms are favorable, which is why both numbers matter for different questions.
The IRS allows you to deduct a portion of your property's value (excluding land) each year as depreciation, reducing your taxable rental income even though you haven't spent that money in cash that year. The [Depreciation Calculator](/depreciation-calculator/) applies the standard 27.5-year residential rental depreciation schedule to estimate your annual deduction — a real tax benefit that materially improves your after-tax return beyond what cap rate or simple ROI figures show.
Yes — this is called depreciation recapture, and it means the depreciation you deducted over the years is taxed (typically at a maximum 25% rate) when you sell, since the IRS is effectively recovering the tax benefit you received annually. Track your cumulative depreciation from the [Depreciation Calculator](/depreciation-calculator/) over your ownership period so you aren't surprised by this liability at sale time — it doesn't erase the benefit, but it does mean the deduction is partly a tax deferral, not a permanent tax elimination.
Property tax rates vary enormously by county and state, commonly ranging from under 0.5% to over 2% of assessed value annually, and this is a recurring cost that directly reduces your net operating income. Use the [Property Tax Calculator](/property-tax-calculator/) with the specific property's assessed value and local rate before finalizing your cap rate or ROI estimate — a property that looks attractive using a national-average tax assumption can look very different once you plug in your specific county's actual rate.
If you're responsible for common-area or master-metered water costs (common in multi-unit buildings), your actual water usage and cost is a real, recurring operating expense that affects net operating income the same way property tax does. The [Tank Volume Calculator](/tank-volume-calculator/) and [Pipe Volume Calculator](/pipe-volume-calculator/) help estimate water system capacity and usage patterns when evaluating a property with shared water infrastructure, particularly relevant for older multi-unit buildings with a single shared water heater or supply line.
Older buildings often have plumbing sized for a different era's usage patterns, and undersized supply lines or aging tanks are common sources of tenant complaints and maintenance calls. The [Pipe Volume Calculator](/pipe-volume-calculator/) and [Tank Volume Calculator](/tank-volume-calculator/) help you understand whether existing infrastructure (a shared hot water tank, for instance) is adequately sized for the number of units it serves, informing a maintenance reserve estimate before you buy rather than after tenants start complaining.
Use cap rate to compare properties as unleveraged assets (useful when comparing across different financing scenarios or all-cash purchases), and use the [Rental Property ROI Calculator](/rental-property-roi-calculator/) for cash-on-cash return when you want to know your actual return on the cash you're putting in, given your specific financing terms. They answer different questions — a property with a lower cap rate might still have a higher cash-on-cash return if financed favorably.
Many jurisdictions reassess a property's taxable value at sale price, which can mean your property tax bill increases meaningfully in year one compared to what the previous owner paid — a common surprise for new landlords who budgeted based on the seller's tax bill. Re-run the [Property Tax Calculator](/property-tax-calculator/) using the actual purchase price and your local jurisdiction's reassessment rules, not the prior owner's tax history, before finalizing your cash flow projections.
For an older tank serving multiple units, a proactive replacement during a planned vacancy avoids an emergency call (often at a premium rate) and potential water damage from a failure. Use the [Tank Volume Calculator](/tank-volume-calculator/) to confirm the replacement tank is sized correctly for current occupancy — buildings often have more units or higher usage than when the original tank was installed, making a like-for-like replacement sometimes inadequate.
Start with the [Cap Rate Calculator](/cap-rate-calculator/) for a quick unleveraged screening comparison across candidate properties, then run your top candidates through the [Rental Property ROI Calculator](/rental-property-roi-calculator/) with your actual financing terms, subtract realistic [Property Tax Calculator](/property-tax-calculator/) and maintenance estimates (informed by plumbing age via the volume calculators), and factor in the [Depreciation Calculator](/depreciation-calculator/) tax benefit — the property with the best combined picture across all four, not just the highest single number, is the stronger buy.
The financial calculators (cap rate, ROI, depreciation, property tax) work identically regardless of unit count, since they're based on income, expenses, and purchase price rather than property type. The plumbing volume calculators become more relevant specifically for multi-unit buildings with shared water infrastructure — a single-family rental's water system is a much smaller, less shared-cost consideration.