Gross Profit Margin Basics

Sales can grow while a business quietly gets poorer. The calendar is full, revenue is up on last year, and yet there is less left over each month than there used to be. When that happens, the first number to check is not sales — it is gross profit margin, because it tells you how much of every dollar of sales actually survives the cost of delivering the work.

What gross profit margin measures

Gross profit is what remains after you subtract the direct costs of delivering your product or service — materials, stock, subcontractors, freight, and the wages of people doing the billable work itself. Gross profit margin is that figure expressed as a percentage of sales: gross profit divided by sales. It deliberately ignores overheads such as rent, insurance and admin wages, because it is answering a narrower question — is the work itself profitable, before the cost of running the business around it?

Why comparing across industries misleads

A supermarket survives on a thin gross margin and enormous volume. A consultant with almost no direct costs can show a gross margin near the top of the scale and still lose money once overheads land. Neither figure says anything about the other business. Comparing your margin with a friend in a different industry is close to meaningless; the comparisons that matter are your own margin over time, and businesses doing genuinely similar work at a similar scale.

Break it down by product line or job type

A single blended margin can hide the real story. One profitable service line can quietly subsidise another that loses money on every sale, and the total looks acceptable throughout. Tracking categories in Xero or MYOB — by product line, service type or job — let you see margin where decisions are actually made. For project-based businesses, simple job costing does the same thing: quoted price against actual materials, subcontractors and hours, job by job.

Why margins drift down

• Costs rose and prices did not. Supplier increases arrive a few dollars at a time and rarely trigger a repricing decision, so the erosion compounds quietly.
• Quotes missing items. Travel time, waste disposal, consumables, small materials — costs that are real on every job but absent from the quote template.
• Discounting without a rule. Ad hoc discounts given at the point of sale come straight out of gross profit, and nobody adds them up until year end.
• Unbilled variations. Extra work done in good faith on fixed-price jobs, delivered but never invoiced.

What we commonly see go wrong

• Direct costs coded to overheads, or overheads coded to cost of sales, so the margin moves for bookkeeping reasons rather than business ones.
• Owners watching the profit-and-loss total and never the margin percentage, so growth hides the erosion underneath it.
• No job costing on larger projects, so nobody knows which jobs made money until long after the pricing lesson could have been applied.
• Stock counted rarely, which turns cost of goods sold into a guess for most of the year.

A worked example

As an illustration: a landscaping business grows its sales strongly, yet the owner takes home less than before. The blended gross margin has slipped — say from around 45% to about 38% — because supplier prices rose several times while quoted rates stayed fixed, and unbilled variations crept in on the bigger jobs. Splitting the margin by job type shows regular maintenance work holding steady while construction projects did the damage. The fix is not more sales — more sales at that margin would make things worse. It is repricing the construction work, tightening the quote template, and billing variations as they happen.

When to get help

If your margin is drifting and you cannot say which product or job type is responsible, or the split between direct costs and overheads in your file has never been reviewed, it is worth getting the numbers cleaned up before making pricing decisions on top of them. Pricing decisions built on miscoded books tend to fix the wrong problem, and we see that more often than genuine pricing mistakes.

What is a good gross profit margin?

There is no universal figure — a healthy margin in retail would be alarming in consulting, and vice versa. The useful comparisons are your own margin over time and businesses doing similar work at a similar scale. A stable or improving trend matters more than any single number.

Should wages be included in cost of goods sold?

Wages of people directly delivering the billable work — production staff, site labour, subcontractors — generally belong in cost of sales. Admin and management wages belong in overheads. Whichever split you choose, apply it consistently, or your margin trend becomes meaningless.

How often should I review my gross margin?

Monthly is ideal if you run management reports, and quarterly is a sensible minimum. Always look at it before a price change, before taking on a large job, and whenever a key supplier lifts prices.