Calculate Your True Hourly Cost in 4 Steps

Most solo design business owners set their fees on a hunch, then wonder why they work 60-hour weeks and still feel broke. Your true hourly cost is the number that ends the guessing. It tells you the floor beneath every fee you quote, whether you bill by the hour or (better) by flat fee.

Key takeaways

✔Your true hourly cost is your total annual cost divided by the hours you actually bill, not the hours you work. Most interior design principals bill about half the hours they put in, so the real number runs far higher than they expect.

✔ The formula is straightforward: (total annual cost ÷ billable hours) × profit margin. Toggl lays it out the same way in its billable-rate guide.

✔ Interior designers and firm owners typically bill only 20 to 30 hours a week, per Toggl’s research, because marketing, admin, and client communication eat the rest. Pricing as though you bill 40 quietly starves your business.

✔ Knowing your true hourly cost matters even when you never charge by the hour. Use it as a floor, then price the transformation with flat fees so you stop capping revenue at your calendar.

What does “true hourly cost” actually mean for a solo interior design business owner?

Your true hourly cost is what one hour of your working time genuinely costs you to deliver, once you fold in everything you pay to stay in business and everything you want to earn. It is not your desired rate. It is the break-even-plus-profit number that your rate has to clear.

Two buckets feed it. Direct costs are the hours you spend delivering design work, plus project supplies. Indirect costs, your overhead, include rent, software subscriptions, insurance, marketing, accounting fees, and all the administrative time nobody pays you for. Invoicemama’s labor-cost breakdown frames the full picture as base wage plus burden costs plus allocated overhead. For a solo interior designer, you are the wage and the burden and the overhead, all in one person.

Here is where interior design solopreneurs get fooled. QuickBooks notes that the true cost of an employee runs 25 to 40 percent above their base wage once you add taxes, workers’ compensation, and benefits, so a worker at $25 an hour actually costs $32 to $35 before any overhead or profit. You carry those same hidden loads on yourself: self-employment taxes, your own health insurance, retirement contributions, paid time off you never actually take. When you price only against your desired salary, you leave every one of those on the table.

How do you calculate your true hourly cost step by step?

Start with your total annual cost, then divide by the hours you truly bill, then add profit. Toggl’s guide gives the working formula: billable hourly rate = (total costs ÷ billable hours) × profit margin. Walk it in four steps.

1. Add up your total annual cost. Include the salary you want to pay yourself, plus every operating expense: rent, design software, insurance, accounting, marketing, subscriptions, and taxes you cover as an owner.
2. Find your real billable hours. Take the hours you work in a year, then subtract vacation, sick days, and all the non-billable time. This is the step that changes everything (more on it below).
3. Divide cost by billable hours. That gives your break-even hourly cost, the point where you have covered everything and earned nothing extra.
4. Layer on your profit margin. Set a target percentage for your industry (Toggl uses 20 percent as an example) and multiply. That is your true hourly cost, the floor your fees must clear.

Here is an illustrative solo interior designer to make it concrete. The numbers are an example, not a benchmark; run yours.

Line item	Illustrative amount
Salary you want to pay yourself	$120,000
Overhead (rent, software, insurance, accounting, marketing, taxes)	$40,000
Total annual cost	$160,000
Hours worked per year	1,920
Billable hours (about 50%)	960
Break-even cost per billable hour	$166.67
Add 20% profit margin	$200 per hour

At those inputs, this designer needs every billable hour to clear $200 to hit her salary and her margin. If she has been quoting projects that pencil out to $95 an hour of her actual time, she has been running the business at a loss and calling it a busy season.

Why do solo interior design firm owners only bill a fraction of the hours they work?

Because the work that fills your calendar is mostly work nobody pays you for. Toggl’s research puts it plainly: the average solo owner spends roughly 50 percent of their time on marketing, selling, administering, and other non-billable tasks. Work 1,920 hours in a year and you likely bill closer to 1,000. Toggl also finds most full-time freelancers realistically bill only 20 to 30 hours a week.

For a design principal, that non-billable half is sourcing that fell through, the vendor who never called back, the client email thread that spiraled, the proposal you rewrote three times, the bookkeeping you do at 11 p.m. None of it lands on an invoice. When you price as though you bill 40 hours a week, you have quietly agreed to work the other 20 for free and to fund your overhead out of thin air.

Run one more check that stings. Toggl suggests calculating your effective hourly rate on a recent project: total revenue divided by every hour you actually invested, counting each email, meeting, and revision. Pull your last three projects and do it. Most owners are startled at how low the real number is. That gap between what you thought you earned and what you actually earned is the cost of never knowing your true hourly number.

Should you actually charge by the hour once you know your number?

No. Calculate your true hourly cost so you understand your floor, then abandon hourly billing entirely. Hourly is a trap. It caps your revenue at your calendar and trains clients to watch the clock instead of valuing the outcome. The moment you get faster and more skilled, hourly billing punishes you by shrinking the invoice.

Use the number a different way. Let it set a project minimum, the smallest project worth your time, talent, and team, then hold that line. Price the transformation rather than the minutes. Your client is buying a home they will live in 24 hours a day, 365 days a year, for 15 to 20 years. That is the relevant math, not the hours you spent specifying a sofa. A flat fee tied to that result protects your profit and your sanity at the same time.

I lived the shift. I went from 40 clients to 10, from 70-hour weeks to 40-hour weeks, doubled my revenue for the fifth year running, and took my first three-week vacation in five years. Fewer, better projects at fees built on a number I actually understood. Undercharging is almost never a math problem. It is a worth problem wearing a market problem’s clothing. But you cannot stand firmly in your value when you have never done the math to know what your value costs you to deliver.

Once you have your true hourly cost in hand, a complimentary Design Business Assessment is where you map the gap between the fees you charge now and the flat-fee structure your numbers actually support.

Frequently asked questions

How many billable hours should a solo business owner assume per year?
Assume you bill about half the hours you work, not all of them. Toggl’s research shows the average solo owner spends roughly 50 percent of their time on non-billable marketing, selling, and admin, and that most full-time freelancers bill only 20 to 30 hours a week. If you work 1,920 hours a year, plan your pricing around roughly 960 to 1,000 billable hours.

What’s the formula for calculating a true hourly rate?
Billable hourly rate = (total annual costs ÷ billable hours) × profit margin, per Toggl’s billable-rate guide. Total costs include your salary plus all overhead, billable hours are the hours you actually invoice, and the profit margin is a target percentage you set (Toggl uses 20 percent as an example). The result is the floor every fee you quote should clear.

Why is my true hourly cost higher than my hourly wage?
Because your wage ignores taxes, insurance, retirement, and overhead. QuickBooks reports the true cost of an employee runs 25 to 40 percent above their base wage once burden costs are added, so a $25 worker really costs $32 to $35 before overhead. As a solo owner you carry all of that on yourself, which is why your true hourly cost sits well above the salary you want to pay yourself.

Do I still need to know my hourly cost if I charge flat fees?
Yes, and it matters more, not less. Your true hourly cost is the floor that keeps a flat fee profitable. Calculate it so you know your minimum, then set flat fees on the transformation you deliver rather than the hours you log. Get paid for the result, not the minutes.

About Melissa Galt

Melissa Galt is a sought-after business coach, marketing consultant, and keynote speaker who empowers designers to build highly profitable businesses without the burnout. Drawing on three decades as principal of her own successful residential design firm, she helps creative professionals earn more in less time, with less stress.

She is the author of four bestselling books, including Marketing Luxury Design, The Language of Success, Design Discovery, and Proximity to Profits. She also hosts the weekly Design Business Freedom™ podcast, sharing unfiltered advice on mindset, money, and marketing for interior design pros ready to elevate their game. When you’re ready to take your practice to the next level, book a complimentary Design Business Assessment with Melissa.