The essentials in 30 seconds
- The percentage of works sets your fees, not your margin: the margin depends on hours spent, which nobody counts.
- Four steps: complete annual costs, real billable hours (around 1,000 a year solo), floor rate, target rate with a safety margin.
- For a solo studio in the Paris region, the floor rate often sits between €60 and €90 excl. VAT per hour; the market shows €75 to €200. The gap is your margin, or your loss.
- Measure each project phase by phase: forty unplanned site hours are enough to fall below the floor.
- The five margin leaks are all non-billable time: re-typing, reworked estimates, client back-and-forth, manual pricing, chasing.
Why "8 to 15% of the works" says nothing about your margin
Most interior designers set their fees as a percentage of the cost of works, between 8 and 15% depending on the assignment, or as a fixed fee per phase. It is readable for the client and consistent with the value created. But this calculation has a blind spot: it never looks at time. A project with €80,000 of works billed at 12% earns €9,600 excl. VAT, whether it took you 90 hours or 210. In the first case you earn €107 an hour; in the second, €46. And nothing in your invoicing tells you.
The hourly rate is therefore not primarily a billing method: it is a measuring instrument. Even if you never bill by the hour, knowing your floor rate is the only way to know whether a project, a type of assignment or a type of client makes or loses you money. Our guide to interior designer fees details the three fee models; this one deals with what they hide.
Step 1: your annual costs, all of them
The first figure to establish is what it costs for your studio to exist for a year, before paying yourself a single euro. Two blocks.
Fixed costs: software (design, management, estimating, office), professional liability and ten-year insurance, rent or coworking, phone and internet, travel, equipment and its renewal, accountant, training, communication (website, portfolio, trade shows), bank fees. For a solo studio this block commonly sits between €10,000 and €18,000 a year; insurance and software are often the two largest items.
Social contributions and tax: they depend on your status. As a French micro-entrepreneur, contributions are a percentage of turnover collected, in the region of 21 to 26% in 2026 depending on your pension fund and regime, to be checked on the URSSAF website. As a sole trader on the actual regime or as a company, they are computed on profit or remuneration and commonly represent 40 to 45% of net pay. Add a provision for income tax. The exact figure is your accountant's; the order of magnitude is enough for the method.
To these two blocks add the variable only you set: the net income you want. Not the one you hope for, the one below which the business makes no sense to you.
Step 2: your real billable hours
This is the step everyone overestimates. A year has about 218 working days. Remove five weeks of holidays and public holidays, a week of training, a few sick days: around 200 worked days remain, that is 1,500 to 1,600 hours. Of those hours, a large share is not billable: prospecting, first meetings that do not convert, administration, accounting, reading, networking, chasing, answering enquiries that go nowhere. In a solo studio this share commonly reaches 30 to 40%.
The result is lower than one would like: 900 to 1,100 billable hours a year is the realistic range for a sole practitioner. Take 1,000 to start, then measure for a quarter. Overestimating this figure is the first cause of hourly rates that are too low: you divide your costs by hours that do not exist.
Steps 3 and 4: floor rate, then target rate
The floor rate is the result of the division: (fixed costs + contributions and tax + desired net income) / real billable hours. Below this rate, every hour worked costs you money. It is not a price, it is a red line.
The target rate adds a safety margin of 15 to 25%, which absorbs what the floor ignores: projects that run long, unpaid invoices, quiet months, investment in the studio. This is the rate your fees must defend, whatever billing model you show the client. Then confront it with the market: in 2026, hourly rates displayed by interior designers in France range from €75 to €200 excl. VAT depending on city, experience and reputation. If your target rate is below the bottom of that range, you are underpaying yourself; if it is above the top, your cost structure or your volume of hours needs a second look.
Three costed scenarios (orders of magnitude, Paris region, 2026)
| Item | 1. Solo, starting out | 2. Solo, established | 3. Studio of two |
|---|---|---|---|
| Annual fixed costs | €12,000 | €15,000 | €22,000 |
| Estimated contributions and tax | €16,000 | €21,000 | €26,000 |
| Desired net income (owner) | €36,000 | €48,000 | €60,000 |
| Collaborator (fully loaded salary) | — | — | €52,000 |
| Real billable hours | 1,000 h | 950 h | 1,800 h |
| Floor rate | €64 / hr | €88 / hr | €89 / hr |
| Target rate (+20%) | €77 / hr | €106 / hr | €107 / hr |
Two lessons. The studio of two does not have a lower floor rate than the established solo: the second person brings hours, but also a loaded cost and extra fixed costs. And the starting-out scenario, with its €64 floor, explains why so many young studios sell assignments at an implicit €50 an hour: they divided by 1,500 hours instead of 1,000.
A project's real margin, phase by phase
The floor rate is there to measure. Take a finished project, its fees excl. VAT, and rebuild the hours per CFAI phase, even roughly. The example below is a flat with €80,000 of works, 12% fees, that is €9,600 excl. VAT.
| Phase | Planned hours | Actual hours | Gap |
|---|---|---|---|
| ESQ, sketch and mood board | 12 | 16 | +4 (one more variant) |
| APS, outline design | 20 | 22 | +2 |
| APD, detailed design and estimate | 18 | 26 | +8 (estimate reworked twice) |
| PCG, tender documents and DPGF | 10 | 10 | 0 |
| AMT, bid analysis | 14 | 14 | 0 |
| CET, site supervision | 40 | 72 | +32 (delays, surprises, absences) |
| AOR, handover and defects | 6 | 10 | +4 |
| Total | 120 h → €80 / hr | 170 h → €56 / hr | +50 h |
At 120 hours the project earns €80 an hour: above scenario 1's floor, just above the target rate. At 170 hours it drops to €56, below the floor. The project was "profitable" in accounting terms, since the fees were paid; it was loss-making in time terms, and that loss was paid in evenings and weekends. Two items explain most of it: the site, which almost always overruns, and the reworked estimate. The first is protected by the contract (number of site meetings included, hourly rate beyond); the second by method and tooling.
The five margin leaks
All of them are non-billable time slipped into phases billed as a fixed fee.
- Re-typing. The same information (client, property, areas, packages) copied from the prospect record to the estimate, then to the DPGF, then to site tracking. Count thirty minutes to an hour per project, at each step.
- The reworked estimate. An estimate built in a spreadsheet without a price base is redone at every change of brief. With an up-to-date price library you adjust; without one, you start again.
- Untracked client back-and-forth. An approval given by phone, then forgotten, then disputed: that is the APD phase stretching. A dated, time-stamped approval costs a minute and saves hours.
- Manual pricing. Looking up a reference price, calling a tradesperson for a ballpark, comparing three sources: that time is never billed. Our estimating method reduces it; a price base almost removes it.
- Chasing. Chasing a contractor for a bid, a client for a decision, a supplier for a lead time. Individually trivial; over a project, several hours.
Added up, these five leaks commonly represent 15 to 25 hours per residential project. In the example above, removing them brings the project from 170 to under 150 hours, and the effective hourly rate back above the floor. That is margin you do not need to go and ask the client for.
Simulator: your floor rate, your target rate, your margin on a project
Everything is computed in your browser, nothing is sent. The prefilled values match scenario 1 in the table; replace them with yours.
And on a specific project?
And Nodal in all this?
Nodal does not time your hours, and does not claim to. It goes after the five leaks: the prospect record becomes the project with no re-typing, the estimate draws on a price library updated monthly and gets adjusted instead of redone, client approval is online and time-stamped, contractor consultation starts from a common template, and chasing becomes visible instead of guessed. The hours recovered are not extra fees: they are margin that was already yours.