How should interior designers charge?

There are exactly three billing models working designers actually use: a markup on the product you source, an hourly rate (usually prepaid as a retainer), and a flat fee priced by the square foot. Most healthy studios run more than one at once. This guide walks through how each model works, the math behind it, and how to decide which one fits a given project.

Model one: product markup

You buy at trade price, sell to your client at a marked-up price, and the spread is your compensation for sourcing, vetting, and managing the purchase. Markup is usually set per category rather than one blanket number, because the work behind a sofa and the work behind a case of tile are not the same.

Two disciplines make markup work. First, the client sees one number, the client price. If your paperwork ever leaks vendor cost, the conversation stops being about the room and starts being about your margin, permanently. Second, some pieces deserve a fixed price instead of a formula: a one-of-a-kind vintage find or a piece with heavy freight is often better quoted as a single figure you chose deliberately. Keep that exception in your toolkit.

Markup wins when the project is furnishings-heavy. Its weakness is that it earns nothing on the hours you spend on layouts, drawings, and meetings, which is why it is usually paired with one of the other two models.

Model two: hourly, prepaid as a retainer

Straight hourly billing in arrears is how designers end up financing their clients. The version that works is prepaid: the client buys a block of hours up front, your logged time draws it down, and when the block runs low they buy another.

The model lives or dies on two habits: logging time the day it happens (reconstructed timesheets always shrink), and watching the remaining balance so the next block is invoiced before you are working free. If your tooling can bill the refill automatically each month, the model becomes almost self-operating.

Hourly wins for consultations, small scopes, and clients who add rooms as they go. Its weakness is that your income is capped by your calendar.

Model three: by the square foot

A flat design fee calculated on area: square footage times a rate. It is the model high-end residential firms increasingly quote because it prices the outcome rather than the timesheet, and clients understand it instantly.

Rates vary widely with scope, finish level, and market, so treat any number you hear as a starting point, not a benchmark. What matters more than the rate is the structure. Quote per area when rooms differ in intensity (a kitchen is not a hallway). Consider a tiered rate for very large homes, where the second three thousand feet cost less per foot than the first. And bill on a milestone schedule so money arrives as the work progresses.

One rule protects you from every awkward conversation later: once a milestone is invoiced, its amount is frozen. If the scope grows, write a change order that adjusts the remaining milestones instead of quietly editing an invoice the client already saw.

Mixing models is the point

These are not competing philosophies; they are tools for different scopes, and product markup keeps earning no matter which fee model a project runs. A studio might run a square-footage fee on a full renovation, an hourly retainer for a longtime client's refresh, and markup on the furnishings flowing through both. The mistake is not mixing models; it is failing to write down, per project, which model applies.

How to choose, quickly

• Full-home or new build, defined scope: square footage with milestones, plus markup on furnishings.
• Furnishings-led project, light design work: markup does the heavy lifting; add a modest fixed design fee if drawings are involved.
• Open-ended or advisory work: a prepaid hourly retainer, refilled monthly.
• Anything with construction: keep the construction budget separate from your design fee, and track draws and change orders against it explicitly.

The mistakes that cost real money

Unbilled hours past a retainer are the quietest leak in the industry; so are project expenses nobody rebilled and delivered pieces that never landed on an invoice. Whatever tools you use, you need one view that answers "what have we finished but never billed?" on demand. The second classic mistake is editing issued invoices when scope changes instead of writing change orders. The third is markup schedules that have not been reviewed in years while freight and vendor pricing moved on.