Every cost a landlord must account for

The mortgage payment

The mortgage payment is typically the largest single cost for a leveraged landlord.

For an interest-only mortgage, the monthly payment is straightforward: (Mortgage balance x Annual interest rate) / 12.

On a £106,500 mortgage at 5.2%: (£106,500 x 0.052) / 12 = £461/month.

For a repayment mortgage, the payment is higher because it includes capital repayment alongside interest. A repayment mortgage on the same balance at 5.2% over 25 years costs approximately £640/month. The cashflow looks worse, but you are gradually reducing the debt.

Most BTL investors use interest-only mortgages to maximise cashflow. If you do, understand that you have a capital repayment obligation at the end of the mortgage term and need an exit strategy (sale or refinance).

When modelling future cashflow, account for the possibility that rates rise at remortgage. Running a scenario at the current rate plus 1.5% stress-tests the deal against a rate increase.

Letting agent fees

If you use a managing agent, their fee covers finding tenants, collecting rent, handling maintenance queries, and managing the property. This is not free.

Let-only service: 8-10% of the first month's rent (or a fixed fee of £300-£500). The agent finds and places the tenant, then steps back. You manage everything after that.

Fully managed service: 10-15% of monthly rent, ongoing. The agent handles maintenance calls, rent chasing, and day-to-day management. Most landlords with one or two properties in the area they live can manage themselves. Portfolio landlords or those living away from their properties typically use fully managed.

There are additional charges that agents often bury in the small print: - Tenancy renewal fee: £50-£150 each time - Maintenance mark-up: Agents often add 10-15% to any contractor invoice they organise - Inventory preparation and check-out: £100-£200 - Tenancy set-up / referencing: Sometimes charged to landlords as well as tenants

Always read the full terms. A "10% management fee" may be 12-14% once all additional charges are included.

In your cashflow model, use 12% of monthly rent as a catch-all for fully managed service including average additional charges. This is a cleaner estimate than trying to itemise every possible add-on.

Landlord insurance

Standard building insurance is not sufficient for a rented property. You need specialist landlord insurance, which covers:

- Buildings insurance (the structure and fixtures) - Landlord liability (if a tenant is injured due to your negligence) - Loss of rent (if the property becomes uninhabitable due to an insured event) - Legal expenses (optional add-on, but useful) - Accidental damage (optional)

Typical annual cost for a standard terrace: £200-£500/year, depending on the property, location, and cover level. A large HMO with multiple rooms will cost significantly more.

Do not skimp on insurance. A burst pipe rendering the property uninhabitable for three months while repairs are completed can cost £10,000-£30,000 in repairs plus lost rent. Insurance turns that catastrophe into a manageable claim.

In your cashflow model, use £35-£40/month as a baseline for a standard single-let terrace.

Maintenance reserve

This is one of the most commonly omitted costs in beginner cashflow models, and it is the omission that catches landlords out.

Properties need maintenance. Boilers break. Pipes leak. Tenants damage things. Roofs develop problems. Even in a quiet year, there will be maintenance spend.

The standard assumption is a 10% maintenance reserve: set aside 10% of monthly rent each month into a dedicated fund for repairs and maintenance. On £700/month rent, that is £70/month or £840/year.

For older properties (pre-1970s), consider 12-15%. Older plumbing, older electrical systems, and older roofing all cost more to maintain than modern builds.

For properties with an electric heating system rather than gas central heating, maintenance costs are lower (no boiler) but heating bills for tenants are higher, which can affect demand.

Boiler replacement: budget £1,500-£2,500 depending on system type. A combi boiler replacement typically costs £1,800-£2,200 installed. Set aside the maintenance reserve and it will be covered across 2-3 years without affecting cashflow significantly.

Void allowance

A void is a period when the property is unoccupied and generating no rent. Mortgage payments and insurance continue regardless.

In a functioning rental market with good tenant demand, voids of 2-4 weeks between tenancies are common. In lower-demand areas or during slow lettings periods, voids can stretch to 8-12 weeks.

The standard assumption is 4 weeks per year. To convert this to a monthly deduction: (Monthly rent x 4 weeks) / 52 weeks = monthly void provision.

On £700/month: (£700 x 4) / 52 = £53.85/month provision, or £646/year.

Do not model zero voids. Every property will have a void at some point, and modelling without one creates a falsely optimistic cashflow.

In areas with very strong rental demand (city centres with high student or young professional populations), you can model 2 weeks. In lower-demand areas, model 6-8 weeks.

Ground rent, service charge, and leasehold costs

If you are buying a leasehold property (typical for flats and some houses), there are additional costs:

Ground rent: Typically £100-£300/year for older leases. Leases granted after June 2022 have ground rents capped at zero. Ground rents on some older flats are much higher and can escalate - check the lease before buying.

Service charge: Paid to the freeholder or management company for maintenance of shared areas, external repairs, and building insurance. On a leasehold flat, service charges of £1,000-£3,000/year are common. Some purpose-built blocks have charges of £5,000+/year.

Major works contributions: The freeholder can raise a "section 20" notice to fund major works (roof replacement, lift refurbishment, etc.). As a leaseholder you are required to contribute. This can run to thousands of pounds with little warning.

Leasehold flats can still make good investments, but model the full service charge and build a reserve for potential major works contributions. If the service charge is not disclosed clearly by the agent or solicitor, demand it before exchanging.

Accountancy and compliance costs

Running a BTL property, especially inside a limited company, involves annual professional costs.

Accountancy: If you own property in a limited company, you need an accountant to prepare company accounts and file with Companies House. Cost: £500-£1,500/year depending on portfolio size and complexity.

Self-assessment: Even in personal name, HMRC requires you to complete a self-assessment return to declare rental income. If you do this yourself, the cost is your time. If you use an accountant (advisable for anything beyond one property), budget £300-£600/year.

EPC renewal: Energy Performance Certificates are valid for 10 years but will need renewing. Current minimum requirement for rental properties is E rating. Proposed regulations (delayed as of 2026) would require C rating eventually. An EPC assessment costs £60-£120.

Gas Safety Certificate: Required annually by law for properties with gas appliances. Cost: £60-£120/year.

Electrical Installation Condition Report (EICR): Required every 5 years for rental properties. Cost: £150-£300.

In your cashflow model, a catch-all for compliance, accountancy, and certificates of approximately £50-£75/month is reasonable for a single property.

Putting it together: a full cashflow model

Using a £145,000 purchase price, 25% deposit (£36,250), interest-only mortgage at 5.2% on £108,750, renting at £750/month:

Monthly income: £750

Monthly costs: - Mortgage interest: £471 - Letting agent (12%): £90 - Insurance: £35 - Maintenance reserve (10%): £75 - Void allowance (4 weeks): £58 - Compliance and accountancy: £60 - Ground rent / service charge: £0 (freehold)

Total monthly costs: £789 Monthly cashflow: £750 - £789 = -£39

This deal loses money. The property needs to be bought cheaper or rented for more to work.

At £130,000 purchase price with the same rent: - Mortgage on £97,500 at 5.2%: £422/month - Total costs: £740/month - Monthly cashflow: £750 - £740 = £10/month

Still marginal. This is why yield matters so much. Properties with gross yields below 6.5% are difficult to make cashflow-positive in the current rate environment, and require very precise purchase prices to work at all.

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