The two numbers every property investor checks first are the purchase price and the mortgage payment, but these costs rarely damage a portfolio or the expected returns. It is more often the stamp duty surcharge, the empty months between tenancies, the compliance certificates that come round every year, the letting agent’s percentage and the tax bill that arrives long after completion that damage your portfolio.
As a working rule, budget roughly 8% to 12% of the purchase price for the buying costs that sit on top of your deposit, then set aside 20% to 30% of the annual rent for running costs. Deals that only stack up without those figures are not really stacking up at all. Here’s why:
The Purchase Itself Costs More Than the Deposit
The single biggest hidden cost of buying investment property in England and Northern Ireland is stamp duty. The additional property surcharge rose from 3% to 5% on 31 October 2024, and the standard nil-rate threshold went back to £125,000 on 1 April 2025, so the sums are noticeably higher than the ones many investors still have in their heads from a few years ago.
The surcharge applies to the whole price, not just the slice above the threshold. On a £300,000 buy-to-let, that works out at £20,000: 5% on the first £125,000, 7% on the next £125,000 and 10% on the final £50,000. Scotland and Wales run their own versions, so check the rate that applies where you are actually buying.
Then add the smaller items that quietly total a few thousand pounds. According to Rangewell (experts in property financing), financing these purchases often involves comparing a wide range of mortgage products and lenders.
5 Costs Worth Preparing for
- Lender arrangement fees, which are often 1% to 2% of the loan on buy-to-let products, plus a broker fee
- A survey worth having, rather than the valuation the lender does for its own benefit
- Conveyancing, searches and any leasehold enquiry pack, which is usually dearer on a flat than a house
- Furnishing, safety certificates and inventory before the first tenant moves in
- A refurbishment contingency of 10% to 15%, because the second fix always finds something
Void Periods, and the Bills that Keep Arriving
Two or three empty weeks a year is a fair planning assumption for most mainstream lets, and more if you buy in a market with seasonal demand or a lot of new stock. During a void you carry the mortgage, the insurance and, in most cases, the council tax, because the discounts on empty properties are limited and vary by local authority.
Turnover has its own price tag as well. Tenant-find fees, a professional clean, touch-up decorating and the days your agent spends on viewings all land up in the same month. One long-term tenant paying slightly under market rent is frequently more profitable than a churn of tenants paying slightly over it.
Compliance is an Annual Line Item, Not a One-off
Gas safety checks, electrical inspections every five years, EPCs, smoke and carbon monoxide alarms, legionella assessments and deposit protection are all modest individually. Across eight or ten properties they become a predictable four-figure sum every single year, and they are the costs most spreadsheets forget.
Licensing is the bigger variable. Selective licensing and HMO licensing fees differ enormously between councils, and an HMO licence can run to several hundred pounds plus works to meet room sizes and fire standards. Check the local scheme before you offer, not after.
There is more coming. Under the Renters’ Rights Act 2025, all tenancies became rolling periodic tenancies from 1 May 2026, and landlords who fail to give tenants the prescribed Information Sheet risk a fine of up to £7,000. The private rented sector database and the new ombudsman are being rolled out in stages from late 2026, which will bring registration costs and administration time with them. Minimum energy efficiency standards for rented homes are also tightening later this decade, so factor insulation and heating upgrades into your plans for older properties rather than treating them as a surprise.
The Tax You Pay for Growing
Finance cost relief for individual landlords is restricted to a basic rate tax credit, which means higher rate taxpayers can owe tax on profit they have not really made once interest is accounted for. Capital gains tax on residential property is charged at higher rates than most other assets, so exit costs matter when you plan to sell and recycle capital.
Buying through a limited company solves some of this and creates its own costs: typically higher mortgage rates and fees, annual accounts, and often personal guarantees. It suits some portfolios and not others, and the answer genuinely depends on your income, your timescale and how much profit you want to draw. This is the point to pay an accountant who works with property investors, before you buy rather than after.
The Fund Most Landlords Wish They Had Started Earlier
Boilers, roofs, windows, bathrooms and rewires do not fail on a convenient schedule. Setting aside around 1% of the property’s value each year for capital repairs, on top of day-to-day maintenance, turns a £4,000 emergency into a planned expense.
On leasehold flats, read the service charge history rather than the current figure, and ask about planned major works. A £6,000 share of a roof or cladding project can wipe out two years of net income, and it will not show up in the gross yield you were quoted.
How to Budget so the Surprises Stay Small
Model every purchase twice: once on the numbers the agent gives you, and once on a stressed version with a higher interest rate, a month of voids, a 12% management fee and full repair costs. Buy the deals that still work on the second version.
Scale changes the maths too. Once you hold four or more mortgaged properties, lenders treat you as a portfolio landlord and underwrite the whole portfolio, which means tighter stress tests and more paperwork. Growing steadily, with real numbers and a cash buffer, beats growing quickly on optimistic ones.
