The short version
The 50-30-20 rule says a healthy service business spends 50% of revenue on direct job costs, 30% on overhead, and keeps 20% as profit. Your back office lives in that 30%. Grow the usual way and you hire more office staff as you take on more work, so overhead stays pinned at 30% and profit stays stuck at 20%. Automate that admin with Aries and overhead grows far slower than revenue, so the same team carries a bigger book and the profit line climbs past 20%.
Originally posted on the Aries blog page. Aries is built by Tundra AI Labs.
This is part two of a short series where we do the arithmetic instead of hand-waving about productivity. Part one looked at automating quote generation and the hours it hands back. This one zooms out to the whole P&L and one number every owner already tracks, or should: net margin.
There is a well-worn benchmark for what a healthy service business should look like, and it happens to point straight at the part of the business AI is best at shrinking. So let's start with the benchmark, then do the math on what happens to it when the back office stops growing with revenue.
What the 50-30-20 rule measures
The model starts from a 50% gross margin. For a company doing $10 million in annual revenue, the target P&L looks like this:
| Category | Share of revenue | Annual amount |
|---|---|---|
| Revenue | 100% | $10,000,000 |
| Direct costs | 50% | $5,000,000 |
| Gross profit | 50% | $5,000,000 |
| Overhead | 30% | $3,000,000 |
| Net profit | 20% | $2,000,000 |
The value of the rule is that it forces you to separate the cost of delivering a job from the cost of running the company. Messy books blur that line, especially when field labor, payroll taxes, vehicle costs, and owner pay drift between categories. Pick a chart of accounts and apply it the same way every month. A clean, consistent definition matters more than a precise-looking percentage built on shaky bookkeeping.
Read it by trade, not in aggregate
Gross margin isn't one number. It moves with the work. An equipment replacement carries expensive hardware; drain cleaning is mostly skilled labor with little material; a commercial controls project needs engineering and commissioning and often carries retainage; a maintenance agreement has completely different economics from new construction, even inside the same company. So compare service with service, replacement with replacement, residential with commercial, and recurring agreements with one-time jobs. A blended company margin can look fine while one department loses money.
20% is a target, not a given
Twenty percent is a good goal for an established shop, and plenty of companies never get near it, landing somewhere between 5% and 12%, as Contractor In Charge notes in its profit-margin benchmarks for home service companies. The distance between those two worlds is worth serious money. A company at 8% net on $2 million earns $160,000; moving to 12% produces $240,000 without adding a dollar of sales. That four-point swing is $80,000, which is why margin work often beats a bigger marketing budget.
Used as a diagnostic, the rule gives you a first question. If direct costs run above 50%, look at pricing, labor efficiency, purchasing, and job mix. If overhead runs above 30%, look at office staffing, duplicated software, facilities, fleet policy, and marketing returns. That overhead bucket is the one we care about here, because it's where the back office sits, and it's the one that grows every time you win more work.
Why overhead creeps up as you grow
Here's the trap. Direct costs scale with revenue by nature: more jobs need more parts and more field hours, and that's fine, because each of those jobs pays for itself. Overhead is supposed to be the fixed base you spread across a growing top line. In practice it rarely stays fixed, because more jobs also mean more estimates to prep, more invoices to send, more AR to chase, more data to key between systems, and more scheduling to juggle. So you hire another coordinator, then another AR clerk, then another estimator. Revenue doubles and overhead doubles right alongside it, which is exactly why so many growing shops feel busier every year without the profit line moving.
This is the work Aries is built to absorb. It connects to the tools you already run, like QuickBooks and your field service software, and takes over the repetitive admin: prepping estimates, sending invoices at the billing milestone, following up on overdue receivables, moving data between systems, and pulling the reports you can't easily get today. A person still owns the judgment calls; the machine handles the volume.
The effect on the P&L is the whole point. When the back office stops growing in lockstep with revenue, the 30% overhead bucket starts to shrink as a share of a bigger top line, and everything it doesn't consume drops to net profit.
Do the math
Take a shop hitting the benchmark at $5 million in revenue, so 50% direct costs, 30% overhead, and a 20% net margin. Now grow it to $10 million two different ways. Down the first road you staff the office the way you always have, so overhead holds at 30%. Down the second you've automated the repetitive admin, so the office grows slowly and overhead lands near 20%:
Hire linearly
office staff scale with revenue
Automate the back office
office staff held roughly flat
Same $10M in revenue, same 50% direct costs. $1,000,000 more net profit, because the 30% overhead bucket shrank to 20%.
Same revenue, same direct costs, same product going out the door. The only thing that changed is how much of the growth got eaten by back-office headcount. Holding overhead near flat turns a 20% net margin into a 30% one, and on $10 million that's the difference between keeping $2 million and keeping $3 million.
$10M
revenue, up from $5M
20% → 30%
net margin, from a flatter back office
+$1M
net profit, every year
That's an extra $1,000,000 in profit a year on the same revenue, because you grew the top line without growing the back office that supports it.
None of that comes from working the crews harder or squeezing suppliers. It comes from one structural change, where the part of the business that used to grow with every new job stopped growing with it.
The lever: the 50-30-20 rule breaks when overhead scales with revenue. Automating the back office is how you keep that 30% from tracking your growth, so the margin expands as you get bigger instead of standing still.
This turbocharges your people, it doesn't replace them
Worth being clear about what this is not. Holding overhead flat doesn't mean gutting the office. Your coordinators, estimators, and AR staff hold the relationships and make the judgment calls that keep the business running, and none of that goes away. What changes is what fills their day. Instead of keying invoices and re-typing the same data into three systems, they're working the exceptions, chasing the accounts worth chasing, and giving customers a faster answer. The team gets more valuable at the same time the company gets more profitable.
What this looked like at MAC
This isn't a thought experiment. When the owners of MAC Technologies came to us, the goal was blunt: they wanted to 10X the business, without hiring back office staff. That is the 50-30-20 math in one sentence. Aries went in on top of the QuickBooks, Zendesk, and MaintainX they already ran and took over the repetitive admin, so the same office could carry a much bigger book of work: less finished work sitting unbilled, invoices going out sooner, and no new back-office hires as revenue climbed.
Frequently asked questions
What is the 50-30-20 rule for a contractor?
It's a simple target for a service business P&L: 50% of revenue goes to direct job costs, 30% to overhead, and 20% is left as net profit. The first 50% is the cost of delivering the work; the 30% is the cost of running the company; the 20% is what the owner keeps. It's a planning baseline, not a law, and the right split shifts by trade and work type.
Is a 20% net margin realistic?
It's a reasonable goal for a mature, well-run shop, but plenty of home service companies land closer to 5% to 12%. The gap rarely comes from one line. It builds through small leaks across pricing, technician utilization, callbacks, purchasing, office staffing, and uncollected invoices. Overhead is one of the easiest of those to attack, because so much of it is repetitive admin.
Does automating the back office really keep overhead flat?
Not perfectly flat, but close to it. The point is that overhead usually grows in lockstep with revenue, because more jobs mean more estimating, invoicing, AR follow-up, and data entry, so you keep hiring office staff. Automating that work lets the same team carry a much bigger book, so overhead grows slowly while revenue grows fast. That's what pulls the 30% down and pushes net profit up.
Which back-office work can AI actually take over?
The repetitive, rules-based work that lives across your systems: pulling and formatting estimates, sending invoices at the billing milestone, chasing overdue AR on a schedule, moving data between QuickBooks and your field service software, and building the reports you cannot easily pull today. It reads and writes to the tools you already run and flags the judgment calls for a person, so nobody gets replaced and the tedious hours come back.