How long is a piece of string? Apart from the emotional cost that only you can judge, this answer focuses on what you need to consider for the financial cost.

Premises costs could be nothing if you intend to work from your existing spare room at home, or significant if you feel you need swanky offices to impress your clients. If working from home, ensure that your lease, covenants, planning usage restrictions or mortgage lenders don’t prohibit this. You may need your mortgage lender’s or landlord’s approval.

Financing cost depends on whether you have to borrow money to fund your business venture — not just the initial capital cost, but also cash-flow funding. Even if you are funding this from your own savings, you should allow for the opportunity cost to you of not being able to invest that money elsewhere, based on at least the bank savings rate.

Then there are the capital equipment costs for buying office equipment you will need to operate. This includes computer, printer, scanner, telephone, as well as a desk, chair, storage, and perhaps an old-fashioned drawing board!

The technical guidance and support you will need to buy includes the essential office library (printed books and/or online service) of Building and Planning Regulations, NBS specification, plus technical reference books.

There will be the cost of registering your business name and setting up as sole trader, company or limited liability practice. It would also be wise to engage legal, accounting and tax advisers to set up and help you run your business.

Promotion and marketing investment should also be as much as you can afford, and will be proportionally higher when starting up to make clients aware that you are in business. This includes a website (now essential) and possibly a brochure or marketing material, PR and press coverage — you may wish to engage a PR consultant for this— plus entertaining and networking with clients.

There will also be set-up costs for your logo, stationery, signboards and so on, which again can be as elaborate or as simple and homegrown as you wish.

Operational overheads always cost more than expected, and include professional subscriptions (Arb and the RIBA), insurances (professional indemnity, public liability, property, travel and contents), as well as general expenses and utilities such as broadband and IT support.

You should also allow for training and continuing professional development, and for attending client events and conferences. Signing up for the RIBA Chartered Practice Scheme offers great value at £100 a year for a sole practitioner, for which you can tap into a range of technical support services and marketing for your practice through RIBA Client Services web, directory, and nomination services.

You will probably need to pay yourself a salary to exist on before your first fee income comes rolling in, so that should also be considered in your set-up costs.

Now to answer your question, “how much?” I’ll assume that you have already carried out your in-depth research and sole searching, and have a detailed and convincing business plan all prepared — and that you still want to set up your own practice!

I’ll also assume that you are looking at the most modest start-up level of working from your spare room at home as a sole trader, using your existing savings, furniture and equipment, and producing your own marketing material. Based on this, I reckon the very minimum to get started would be about £3,000, and would more likely be nearer £5,000 for the essential tools and requirements of registration, insurance, and business systems.

The recent RIBA Good Practice Guide, Starting a Practice by Simon Foxall of the Architects Practice (RIBA Publishing, £15), is an excellent source of information to help you find out what you have to do, and how to work out how much it will cost.