Rental Cash Flow Calculator
Work out what a rental property actually leaves each month after the mortgage, management, maintenance, insurance and realistic vacancy.
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Gross rent is not income. What a rental property actually produces is the rent left after the mortgage, management, maintenance, insurance, local taxes and the weeks it stands empty. That figure is frequently negative in high-price markets, which is not automatically bad — but it should be a decision, not a surprise.
Vacancy is the line most often left out. A single empty month costs 8.3% of annual rent, which is usually larger than any other single deduction.
The calculation
Effective rent = rent × (1 − vacancy). From that, subtract the mortgage payment, the management fee (charged on rent actually collected) and maintenance plus insurance. What remains is cash flow.
Worked example
A property renting at 1,600 with an 8% vacancy allowance collects about 1,472 a month. Management at 10% takes 147, maintenance and insurance 150, and the mortgage 950 — total costs of 1,247. Net cash flow is roughly 225 a month, or 2,700 a year.
What is not included
Capital repayment is treated as a cost here because it leaves your account, even though it builds equity rather than disappearing. Income tax on rental profit, letting fees between tenancies and major capital works are also excluded — budget for those separately.
Turn a calculation into an enquiry
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Create your free property pageFrequently asked questions
What vacancy rate should I assume?
Between 5% and 10% in most markets, which is roughly three to five weeks a year. Assuming zero vacancy is the single most common error in rental projections and it flatters the result substantially.
Is negative cash flow always bad?
Not necessarily, but it must be deliberate. A property that costs you money monthly is a bet on capital appreciation, and it needs to be funded from income you can rely on for years, not from optimism.
Should I include mortgage principal as a cost?
For cash-flow purposes yes, because it leaves your account each month. When measuring total return, add it back — it is equity you keep, unlike interest, which is gone.
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