How Rental Income Changes Your FIRE Number

The standard FIRE calculation is built around a single question: how large does your portfolio need to be to fund your expenses indefinitely? The 25x rule answers it cleanly — multiply your annual spending by 25 and that is your number. Simple, portable, widely cited. For a deeper look at FIRE planning with multiple income sources, see the guide to calculating your FIRE number with multiple income sources.

The problem is that it assumes your portfolio is the only income source in retirement. For people with rental properties, that assumption is wrong, and the error is not small. Rental income that covers even a portion of your annual expenses dramatically reduces the portfolio balance you need to retire — sometimes by hundreds of thousands of dollars, sometimes by more than half.

Understanding exactly how rental income changes your FIRE number requires modeling it correctly, which most calculators cannot do.

The Basic Math: How Rental Income Reduces Your Required Portfolio

The 25x rule is derived from the 4% safe withdrawal rate — the idea that a diversified portfolio can sustain annual withdrawals equal to 4% of its starting balance indefinitely. If you need $80,000 per year, you need $2,000,000 (80,000 divided by 0.04).

Now introduce rental income. Say your rental property generates $24,000 per year in net income after mortgage, taxes, insurance, and maintenance. Your portfolio only needs to cover $56,000 per year instead of $80,000. At the 4% rule, that requires $1,400,000 — not $2,000,000. The rental income cut your required portfolio by $600,000.

That $600,000 gap is not a rounding error. It represents years of additional saving and working that you can skip because the rental income is covering the difference. For someone saving $40,000 per year, that is 15 years of contributions. The rental property did not just supplement the retirement plan — it potentially accelerated it by a decade or more.

Net Income Is the Only Number That Matters

The calculation above uses net rental income — after all expenses. This is where a lot of people go wrong when incorporating rental income into their FIRE plan. They use gross rent, or they undercount expenses, and they end up with an inflated income figure that makes their FIRE number look more achievable than it actually is.

The expenses that reduce gross rent to net income include the mortgage payment (principal and interest), property taxes, insurance, maintenance and repairs, property management fees if you use a manager, vacancy allowance, and capital expenditure reserves for major repairs like roofs, HVAC, and appliances.

Maintenance and capital expenditures are the most commonly underestimated. A common rule of thumb is to reserve 1% of the property's value per year for maintenance — on a $400,000 property, that is $4,000 per year. Over a 20-year retirement, deferred maintenance and capital replacements add up quickly, and not reserving for them produces an income figure that looks strong on paper until the roof needs replacing.

The net income figure that goes into your FIRE calculation should reflect a realistic long-run average, not the income from a good year with no major expenses.

The Inflation Question

Unlike a fixed annuity or a pension without a COLA, rental income generally keeps pace with inflation over time. Rents tend to rise with the cost of living, which means the real purchasing power of your rental income stays relatively stable across a long retirement.

This is a meaningful advantage over fixed income sources. A pension paying $2,000 per month in 2025 with no COLA is worth significantly less in real terms by 2045. Rental income at $2,000 per month in 2025 might be $3,200 per month by 2045 if rents track inflation at 2.5% annually — the same real purchasing power, more nominal dollars.

When modeling rental income in your retirement plan, you can reasonably assume it grows with inflation — typically 2% to 3% annually — rather than staying flat. This makes it more valuable in the long run than a fixed income source of the same initial amount.

The Mortgage Payoff Inflection Point

If your rental property still has a mortgage, the net income figure today is lower than it will be once the mortgage is paid off. This creates an inflection point in your retirement income that is worth modeling explicitly.

Say your rental generates $2,500 per month in gross rent. Your mortgage payment is $1,400 per month. After taxes, insurance, and maintenance reserves, your net income is roughly $600 per month — $7,200 per year.

When the mortgage is paid off in 12 years, the same property generates $2,500 minus taxes, insurance, and maintenance — roughly $1,700 per month, or $20,400 per year. The mortgage payoff nearly triples your net rental income from that property.

If you are planning to retire before the mortgage is paid off, your FIRE number needs to reflect the lower net income figure during the mortgage period, not the higher post-payoff figure. A plan that uses the post-payoff income number but retires before the payoff date is working with the wrong inputs. The rental income retirement calculator lets you model both phases separately.

Vacancy and the Reliability Problem

Rental income is not as reliable as a pension or Social Security. Properties go vacant. Tenants stop paying. Markets soften. The income stream has real volatility that a 401k balance, for all its market risk, does not.

For FIRE planning purposes, this means you should not rely on rental income to cover 100% of your expenses. A plan where the rental covers everything and the portfolio is a backup works until there is a six-month vacancy or a major repair that wipes out a year of net income. The portfolio needs to be large enough to absorb periods where the rental income drops or disappears temporarily.

A reasonable approach is to use a conservative net income figure — assuming 8% to 10% vacancy even if your historical vacancy has been lower — and maintain a portfolio that can cover your full expenses if needed. The rental income then functions as a buffer that reduces normal withdrawals, not as a primary income source the plan depends on completely.

When Rental Income Starts Matters

If you own a rental property now but it is not cash-flow positive yet — because the mortgage is high or the market rent in your area does not support strong yields — the income may not materialize until later in your retirement. In that case, you need to model the income as starting at a future age, not from day one of retirement.

The same logic applies if you plan to buy a rental property before retirement but have not yet. The income from a property you own at 58 starts at 58, not at your planned retirement age of 52. Modeling it as starting at 52 overstates how much the portfolio needs to cover in the early years of retirement.

Start age matters for rental income for the same reason it matters for any retirement income source: the years immediately after leaving work are the most expensive years for your portfolio, and income that does not start until later provides less protection for that early withdrawal window.

How to Model It Accurately

To incorporate rental income correctly into your FIRE plan you need a calculator that can handle income with a start age, an inflation adjustment, and a flag for whether it continues indefinitely. A calculator that adds a fixed "other income" number to your retirement income without these features will give you an imprecise answer.

At NumberToRetire.com, the Additional Income section handles rental income directly. You enter the annual net income, the age it starts, whether it adjusts for inflation, and whether it continues after your formal retirement date. You can add multiple properties independently if you have more than one, each with its own start age and income amount. The projection shows rental income as a separate line in the chart alongside your portfolio balance, so you can see clearly how much of your retirement spending it is covering in each year and how that changes over time.

To model the mortgage payoff inflection, use a year-by-year override on the rental income source — set the lower pre-payoff amount for the early years and the higher post-payoff amount starting at the year the mortgage clears. That gives you an accurate picture of when your portfolio needs to cover the gap and when the rental takes over more of the load.