The moment a designer actually calculates their cost of doing business for the first time, something shifts. Projects they thought were profitable turn out to be break-even. Hourly rates that felt reasonable turn out to be below what the business needs to sustain itself. It is not a comfortable realization, but it is a clarifying one.
A member of Interior Design Community described exactly this experience: “I realized I had never fully calculated my cost of doing business, which made me question everything about how I price.” That kind of reckoning is actually a good sign. It means you are ready to run the business like a business.
What “Cost of Doing Business” Actually Means
Your cost of doing business (CODB) is the total of everything it costs to keep your firm operational before you pay yourself a single dollar. It is not what you spend on a single project. It is your ongoing overhead: all the fixed and variable costs that exist whether or not you are billing a client.
For most interior design firms, CODB covers a predictable set of categories: rent or a home office allocation, software subscriptions, professional liability and general liability insurance, payroll or contractor costs, professional memberships (ASID, IIDA, NKBA), marketing and advertising spend, sample library maintenance and materials, vehicle and travel, phone and utilities, banking and processing fees, bookkeeping and accounting fees, and self-employment taxes. If you have employees, add employer payroll taxes and any benefits you provide.
Actually compiling that number takes a few hours, not a finance degree. Pull your last 12 months of bank and credit card statements and sort every expense into one of those categories. Total each column, then divide by 12. That gives you your average monthly CODB. Some designers find their number is higher than expected because they had never seen all the categories side by side before. Others find it lower, which is useful information too, because it may mean they have been underestimating how lean they actually run.
Once you have an accurate monthly CODB number, you have the denominator you need to price correctly. Divide that total by your realistic billable hours per month, and you have the floor: the minimum you need to earn per billable hour just to keep the lights on, before profit and before paying yourself a market-rate salary.
This is the number @damngooddesigner refers to as “your cost to be open”:
“I review my P&L once a week and client P&Ls every other week. We do a quarterly expense squeeze too, when you’re busy, a firm can get the better of you, so we sit down with the team and review to make sure it’s tight. Your cost to be open number is the first thing I want to know when working with a designer, as it tells me a lot about their business.”
The phrase “cost to be open” is precise for a reason. It makes clear that this is not a project metric. It is the business’s operating baseline, and it exists independently of whether any client project is active at any given moment.
Why Most Designers Haven’t Done This
The exercise sounds simple. Many designers have not run it yet. @francisinteriors named why:
“Many of us come into this field as creatives, and the financial side can feel intimidating. I certainly did. I didn’t fully understand what a profit and loss statement or balance sheet was until about six years ago.”
That is a common arc. Design training focuses on spatial thinking, aesthetics, material knowledge, and client communication. Finance is usually self-taught, often late, and often only after a difficult project or a slow quarter forces the issue.
The other reason designers skip the calculation: it forces accountability. Once you know your CODB, you also know whether your current rates are sufficient to cover it. That can be an uncomfortable answer, especially for designers who set their rates early in their careers and have not revisited them since. Raising rates means having a conversation with existing clients or holding firm on new ones, and that pressure often makes avoidance feel easier than clarity.
Avoiding the number has a cost, though. Firms that operate without a clear CODB tend to undercharge in ways they do not recognize until the books show a problem. They accept project terms that look fine on paper but do not hold up once real overhead is factored in. They feel busy but remain unclear on whether being busy is actually profitable. The Small Business Administration consistently identifies not tracking overhead as one of the core financial risks for small business owners, and interior design firms are not exempt from that pattern.
The good news: the CODB exercise does not require an accounting background. It requires a spreadsheet, your bank and credit card statements, and a few hours. @bethany.adams.interiors found a practical way in:
“I copied a template from Google Sheets: annual business budget. It’s easy to fill in and I keep updating as I get new info, projects, expenses, employees. First time I’ve done it and it’s helping me.”
A Google Sheets template works fine. A spreadsheet you build from scratch works too. What matters is doing it, not the tool you use to get there. For designers looking to build stronger financial systems from the ground up, the Let’s Talk Designer Bookkeeping episode (To-The-Trade) with Heather Randell covers practical systems for tracking income, expenses, and understanding your numbers as a small design firm.
The P&L Review: Making CODB an Ongoing Habit
Calculating your CODB once is useful. Reviewing it monthly is how you actually run a business.
Your CODB is not a static number. Insurance renews, sometimes at higher rates. Software pricing changes. You add a contractor during a busy quarter. You expand your sample library. Any of those shifts changes your overhead, and if you are not checking your P&L regularly, those changes can quietly erode the margin you built into your pricing without any single change feeling significant enough to notice.
@francisinteriors made the case directly:
“Understanding your cost of doing business should live inside your monthly profit and loss review. It’s what informs how you price, how you grow, and ultimately how you sustain the business. Once you start reviewing it regularly, it stops being abstract and becomes insight. That’s where real control begins. And this is where you will feel you’re actually a business owner and the CEO of your own company, regardless of the size of your firm.”
The monthly P&L review does not need to be elaborate. At a minimum, it should confirm that your income covers your CODB, with room left over for owner compensation and profit. If that margin is shrinking, the P&L tells you where to look, whether that is rates, billable hours, overhead creep, or some combination of the three.
@marsha_sefcik described the minimum floor:
“You should be tracking your operating expenses, your income, sales, etc., without that information you’re unable to tell if your business is making money. At the very least, you should be looking at your balance sheet and your profit/loss/income statement.”
If you have a bookkeeper, this review takes 30 minutes a month. If you are doing it yourself, it takes longer, but it is worth setting a recurring calendar block for it. The habit matters more than the sophistication of the tool you use to track it.
How CODB Changes Your Pricing
Once you know your CODB and your realistic billable hour capacity, the pricing math becomes straightforward.
A simplified example: if your monthly CODB is $6,000 and you can realistically bill 80 hours per month, your break-even hourly rate is $75. That number represents the floor, not a pricing target: the rate below which you are operating at a loss before you have paid yourself anything. Add a market-rate salary equivalent for your role and a 20% profit buffer, and the actual required hourly rate climbs considerably from that starting point.
This is why designers who have run their CODB often realize their rates are lower than the business requires, not because they undervalued themselves emotionally, but because they were pricing without the underlying data. For a step-by-step approach to building your rate from this foundation, Minimum Hourly Rate for Interior Designers walks through the full calculation. And Monthly Revenue Targets for Interior Designers shows how to set a revenue goal that works backward from your actual cost structure.
CODB also matters for flat-fee work. If you are pricing a project as a flat fee, that fee needs to account for your anticipated hours multiplied by your required hourly floor, plus materials coordination time, client revision cycles, and a contingency buffer for scope drift. Pricing a flat fee without knowing your CODB means the number is essentially a guess, and the guess tends to run low when the project runs long.
Flat-fee, hourly, or hybrid, the structure matters less than whether your pricing is built on what your business actually needs to earn. CODB is what makes that calculation possible in the first place.
The Quarterly Expense Squeeze
@damngooddesigner mentioned a practice worth building into your firm calendar: the quarterly expense audit.
Expenses accumulate when a firm is busy. A software subscription was added during a growth phase. A service used on one project and never canceled. An insurance policy that auto-renewed at a higher rate without triggering a review. Running a quarterly line-by-line audit of every recurring expense, looking specifically for duplicates, unused tools, and costs that have drifted upward without a corresponding increase in value, is the discipline that keeps your CODB from expanding without your awareness.
A few categories worth checking every quarter: software and SaaS subscriptions, contractor retainers or standing commitments, trade memberships and publication subscriptions, marketing and advertising tools, and any recurring services tied to specific projects that should have been canceled once the work wrapped. If you have staff, this exercise is worth doing as a team. It builds shared awareness of what the firm costs to run and tends to surface expenses that individual team members signed up for separately without realizing there was an overlap.
The goal is not to cut costs as a default strategy. It is essential to stay informed on exactly what your firm spends so that every recurring expense still earns its place in the budget. Beyond expenses, Bookkeeping Red Flags for Interior Designers reveals the patterns that tend to surface when firms look at their books with fresh eyes.
Know the Number, Run the Business
The shift from a designer running a business to a CEO of a design firm is partly a matter of mindset and partly of mechanics. The mechanics start with knowing your numbers. The CODB calculation is where that process begins, and the P&L review habit is what keeps it useful over time.
Run it once this week. If you have a bookkeeper, ask them to pull your last 12 months of operating expenses and build the monthly average with you. If you do not, open a blank spreadsheet, pull your bank statements, and start listing. It takes a few hours and changes how you evaluate every project you quote after it.