A margin is profit expressed as a percentage of revenue — profit per dollar sold. There are three that matter, they nest inside each other, and each one confesses a different sin when it slips. Owners who track all three can diagnose a bad month in minutes. Owners who track only "profit" know something's wrong and not where.
All three come straight off a P&L with clean COGS/overhead sorting (previous lesson — do that first).
Say a month looks like: revenue $50,000; COGS $30,000; overhead $14,000; interest and tax $2,000.
Gross margin = (revenue − COGS) / revenue. Here: ($50,000 − $30,000) / $50,000 = 40%. Forty cents of every revenue dollar survives delivery. This is the margin of your product and pricing. It moves when input costs move, when discounting creeps, when jobs run long, when your mix shifts toward worse offerings. It does not care about your rent.
Operating margin = operating profit / revenue. Operating profit is gross profit minus overhead: $20,000 − $14,000 = $6,000, so 12%. This is the margin of your whole machine — product economics and the cost of the company around it. Gross margin steady while operating margin slides means delivery is fine and the overhead base is bloating.
Net margin = net profit / revenue. After interest and taxes: $4,000 / $50,000 = 8%. What the owner actually keeps per revenue dollar. It adds the financing story — a fine operating margin dragged down here means debt service is eating the business.
Notice the structure: each margin equals the one above it minus one specific layer of cost. That's the diagnostic power — when a lower margin falls, find which layer moved.
Gross margin falling → the sin is in delivery or pricing. Supplier increase you didn't pass through, quiet discounting, jobs running over scope, product mix drifting cheap. Fixes: reprice, renegotiate, tighten scope, kill the worst offering. The pricing lessons in this pillar are the toolkit.
Gross steady, operating falling → the sin is overhead. Something below the gross-profit line is growing faster than revenue — subscriptions, admin hires, rent, ad spend that isn't converting. Scan the overhead lines against last quarter; the culprit is visible in one pass.
Operating steady, net falling → the sin is financing. Interest is climbing (rate reset, growing balance) or the tax picture changed. This one is a conversation with your lender or CPA, not an operational fix.
All three healthy but the bank account thin → not a margin problem at all; that's the profit-vs-cash gap. Different lesson, different tools.
The honest answer: it depends on the model, and cross-industry comparisons mislead. A grocery store and a software company can both be excellent businesses at wildly different gross margins, because their overhead structures differ just as wildly. The comparisons that actually inform decisions:
If you want an external benchmark, get it from your industry's trade association data rather than folklore.