Rental cashflow

Rental cashflow is the net sum of money a landlord receives from a rental property after all costs associated with owning and operating it have been paid. It is calculated monthly and expressed as a simple figure. Income minus outgoings. If income exceeds outgoings, cashflow is positive. If outgoings exceed income, cashflow is negative, meaning the landlord is subsidising the property from other funds each month.

The formula is: monthly rental cashflow = gross rent received minus total monthly outgoings.

What counts as income in the cashflow calculation

Gross rent is the primary income component. HMRC's Property Income Manual makes clear that rental income also includes any sums received for the use of furniture, charges for services such as cleaning communal areas, and any payments the tenant makes directly for costs that are ordinarily the landlord's responsibility. In practice, for most self-managing landlords, gross rent is the only meaningful income line, but HMO landlords who include bills in the rent, or who charge separately for parking or storage, should include those figures too.

What expenses reduce cashflow

Every regular outgoing reduces cashflow. The main categories for a buy-to-let landlord are:

Mortgage payment - typically the largest single outgoing. On an interest-only mortgage, this is the monthly interest charge. On a repayment mortgage, it is interest plus principal; note that only the interest element is deductible against rental income for tax purposes under Section 24, not the full payment.

Landlord insurance - buildings and contents (where furnished) coverage.

Letting agent fees - where applicable, typically 8–15% of monthly rent for full management.

Maintenance and repairs - actual costs as incurred, plus a prudent monthly provision for future works. From working with self-managing landlords across the UK, we find that landlords who budget 10–12% of annual rental income for maintenance are rarely caught short; those who budget nothing are routinely exposed when a boiler fails or a roof needs attention.

Compliance costs - gas safety certificate, EICR, EPC renewal, licensing fees where applicable, these are annual or periodic outgoings best expressed as a monthly equivalent for cashflow modelling purposes.

Void periods - the proportion of time the property is unoccupied earns no income but continues to incur mortgage, insurance, and council tax costs. A realistic cashflow model applies a void assumption of at least 5% of annual rent, higher in areas with weaker tenant demand.

Accountancy and professional fees - relevant where the landlord uses a tax adviser or property accountant.

August's expenses tracking feature categorises every outgoing automatically, so your actual cashflow figures are always current without manual reconciliation.

Positive and negative cashflow

A property with positive cashflow generates a monthly surplus after all costs. That surplus can be retained as income, reinvested in the property, or used to service other investment costs. Positive cashflow is the foundation of a sustainable rental business, it means the property is paying for itself and generating a return on the landlord's capital.

Negative cashflow means the landlord is topping up the property each month. This is not necessarily a sign of a failing investment: some landlords accept negative monthly cashflow in the expectation of capital growth outperforming the monthly shortfall over time. But negative cashflow creates ongoing financial pressure and reduces a portfolio's resilience to interest rate rises, void periods, or unexpected repair costs. Landlords using August consistently tell us that the landlords who struggle most during periods of rising mortgage rates are those who never modelled their cashflow at all — they let the property and assumed the rent covered everything.

Cashflow and rental yield: the distinction that matters

Cashflow and rental yield are related but distinct: yield expresses annual income as a percentage of property value; cashflow tells you whether there is money left in your account each month.

A property can have a strong gross yield and still produce negative cashflow, for example, if the mortgage rate is high, the letting agent fee is substantial, or the property has significant running costs. Conversely, a property purchased without a mortgage may show modest yield but excellent cashflow because there is no debt service reducing the monthly surplus. Neither metric is superior: yield helps you compare investment opportunities; cashflow tells you whether you can afford to hold what you already own.

The rental cash flow calculator on August lets you model monthly cashflow across different mortgage rates, void assumptions, and expense scenarios before committing to a purchase or rent review.

The impact of tax on cashflow

Cashflow as calculated above is a pre-tax figure. The actual money available to the landlord after tax depends on their income tax rate, the structure through which they hold the property, and how allowable expenses interact with their tax position.

The most significant cashflow consideration for leveraged landlords is the Section 24 mortgage interest restriction. For higher-rate taxpayer landlords, Section 24 means tax liability can exceed the apparent monthly surplus, turning a nominally positive cashflow into a net loss after tax. A landlord paying 40% income tax on profits calculated without full mortgage interest relief can find that a property showing £200 per month positive cashflow in fact costs them money after the tax bill is settled. This is one reason why many higher-rate taxpayer landlords have restructured their portfolios into limited company ownership, where corporation tax applies and full mortgage interest deductibility is preserved.

Cashflow modelling that ignores tax is incomplete. Always calculate both gross monthly cashflow and estimated after-tax cashflow before making investment decisions.

How to improve rental cashflow

The levers available to a landlord are income, costs, financing, and tax efficiency.

On the income side: reviewing rent against local market rates at each renewal, reducing void periods through good tenant selection and prompt re-letting, and eliminating any services that increase management cost without a corresponding rent premium.

On the cost side: remortgaging to a more competitive rate, switching to self-management where agent fees are disproportionate to the service delivered, and keeping maintenance costs down through preventative upkeep rather than reactive repair.

On financing: interest-only mortgages produce better monthly cashflow than repayment mortgages for the same property, though they leave the capital debt outstanding. Many landlords use interest-only financing to maximise monthly cashflow and plan to repay from eventual sale proceeds or accumulated rental profits.

For a practical guide to categorising every expense correctly, from mortgage interest and insurance to maintenance and service charges, see our rental property expense categorisation guide.

Frequently asked questions

What is a good rental cashflow figure for a buy-to-let property? 

There is no universal benchmark, but most UK buy-to-let landlords target at least £200–£300 per month positive cashflow per property after all costs and before income tax. The figure varies significantly by purchase price, mortgage level, location, and property type. A property in the north of England purchased at a lower price point may generate £400–£600 per month; a higher-value London property with a large mortgage may produce minimal monthly surplus even at a good gross yield. The more useful question is whether the post-tax cashflow, factoring in all realistic expenses and a void allowance, still justifies the capital and management time committed.

Is rental cashflow the same as rental profit? 

No. Cashflow measures the actual movement of money in and out of the landlord's account each month. Profit, in the accounting sense, also accounts for depreciation, capital movements, and other non-cash items. For most small landlords the difference is modest in practice, but the distinction matters when filing a tax return: allowable deductions for HMRC purposes follow specific rules set out in HMRC's Property Income Manual and do not always match the expenses that affect monthly cashflow. Mortgage principal repayment, for example, reduces monthly cashflow but is not a deductible expense against rental income.

How does a void period affect cashflow? 

During a void period, rental income falls to zero but most fixed costs, including mortgage payments, insurance, standing charges, continue. A property that produces £300 per month positive cashflow in occupation will typically cost £600–£1,000 per month during a void once mortgage and insurance costs are included. A realistic cashflow model accounts for void periods explicitly, rather than assuming 100% occupancy, and maintains a cash reserve sufficient to cover at least two to three months of voids without requiring the landlord to fund the shortfall from other income.