Post-Tensioned Slab Design Break-Even: About $81K/Month

Fixed costs $56.0K/mo Monthly overhead base

Contribution margin 61% After variable costs

Break-even revenue $91.6K/mo Monthly target

Break-even timing Month 8 Launch ramp

Break-even calculator

This calculator tests monthly revenue, variable expenses, and fixed costs against break-even.

Lean Base Full

Monthly revenue Revenue sets the pool that covers direct costs and overhead. $ Low sales High sales Variable expenses These are direct costs that rise with each project. $ Low cost High cost

Money available to cover fixed costs $119,983 $159,083 revenue - $39,100 variable expenses

Margin ratio

75%

Covers fixed costs

Yes

Fixed monthly costs This is the monthly cost base break-even must cover. $ Light overhead Heavy overhead

Break-even chart Revenue Total costs

Which expenses are fixed, variable, semi-variable, or semi-fixed for a post-tensioned slab design firm?

Cost classification

Break-even is only useful when fixed overhead, revenue-linked fees, and step-up staffing sit in the right buckets. Here’s the quick math: first-year payroll is $510,000, or $42,500/month, before usage, drafting, insurance, and travel.

Expense	Cost	Break-Even Treatment	Common Mistake
Office Lease	Fixed	Model at $6,500/month from Month 1 through Month 60. It sets the monthly overhead floor before any billable design work is sold.	Tying rent to project count instead of treating it as committed capacity.
Base Professional Liability Insurance	Fixed	Model at $3,500/month as baseline coverage. Keep it separate from project-specific insurance that moves with revenue.	Blending base coverage with project-specific coverage and overstating variable margin.
Salary Payroll	Fixed	Use $42,500/month in the first year, based on $510,000 annual payroll across 4.5 full-time equivalent roles.	Burying revision labor inside overhead instead of showing the hit to project margin.
Project Specific Professional Liability	Variable	Apply 4.5% of revenue in the first year, declining to 3.5% by the mature year. It rises only when project revenue rises.	Modeling it as a flat insurance line and missing revenue-linked risk.
Business Development Travel	Variable	Apply 3.0% of revenue in the first year, declining to 2.0% by the mature year. It should flex with sales activity.	Locking it as monthly overhead even when proposal volume changes.
Software Subscription Usage Fees	Semi-variable	Use 6.5% of revenue in the first year, declining to 4.5% by the mature year. Treat usage as margin pressure tied to project workload.	Calling the full line fixed because the word subscription appears in the name.
External Drafting and Detailing Services	Semi-variable	Use 12.0% of revenue in the first year, declining to 8.0% by the mature year. It scales with outsourced production load and revisions.	Hiding outsourced revision cycles inside general overhead instead of reducing contribution.
Annual Marketing Budget	Semi-fixed	Model as a planned step from $45,000 in the first year to $85,000 in the mature year. It changes by budget stage, not each project.	Treating marketing as a pure percentage of sales and masking acquisition efficiency.

How does break-even change from lean to base to full-capacity post-tensioned slab design work?

Scenario table

Break-even shifts fast as staffing load and scope mix change. The lean case is close to flat, the base case adds a real cushion, and the full-capacity case has the widest buffer if backlog quality and revision control hold.

Planning cases only; actual break-even will move with staffing mix, scope changes, and collection timing.

Scenario	Monthly Revenue	Variable Costs	Fixed Costs	CM Ratio	Operating Profit	Break-Even Signal
Lean launch case	$804k	$209k	$598k	74%	$-3k	Near break-even; small slippage turns loss.
Base growth case	$1,591k	$382k	$814k	76%	$395k	Clear cushion above break-even if backlog stays steady.
Full-capacity case	$3,995k	$719k	$1,402k	82%	$1,874k	Wide margin, but revision control still protects profit.

What breaks the break-even plan for a post-tensioned slab design firm?

Stress test

The plan is basically at break-even, with only about a $3k monthly gap. A 10% revenue miss, a 10% jump in fixed costs, or variable expense rising to 30% each push the firm into a clear loss.

Stress Case	Changed Assumption	Break-Even Revenue	Revenue Gap	Risk Signal
Current plan	No change.	$807k/month	$3k gap	Tiny cushion; one slow month flips it.
Revenue shortfall	Revenue falls 10% to about $724k/month.	$807k/month	$83k gap	Lower intake creates an operating gap.
Fixed-cost pressure	Fixed monthly costs rise 10% to about $657k.	$888k/month	$84k gap	Higher overhead needs more billed work.
Margin pressure	Variable expense rises from 26% to 30%.	$854k/month	$50k gap	More revision hours or liability fees push break-even up.
Combined pressure	Revenue falls 30%, fixed costs rise 10%, and variable expense rises to 30%.	$940k/month	$377k gap	This is the most fragile case; collections and utilization both matter.

Should you lock in the office lease, software, and hires yet?

Founder checklist

Before you lock in the office lease, software, and hires, make sure signed or late-stage work can carry the Year 1 run rate of about $80.4K a month and still keep break-even at Month 8. If demand is soft, hold fixed costs and capex back.

1Backlog$80.4K/mo

Verify signed or late-stage work can cover the Year 1 revenue pace, or the office and hiring plan will outrun demand.

2Package Price$26.4K

Use the modeled rates as your floor: full structural design is 120 hours at $220, value engineering is 40 hours at $275, and construction administration is 15 hours at $185, so weak pricing will squeeze margin fast.

3Burn Rate$56.0K/mo

The opening fixed load is about $56.0K a month, including the $3.5K professional liability policy, so every extra commitment must earn its keep.

4Staff Ramp4.5 FTE

Keep the staffing ramp tied to review capacity, because the Year 1 team already assumes 4.5 full-time equivalent roles before any growth hire.

5Cash Cushion$661K

Hold at least $661K of cash, because the model bottoms in Month 7 and does not reach break-even until Month 8.

6Launch Spend$121.5K

Keep the one-time setup spend for workstations, software licenses, plotting gear, furniture, networking, AV, and the website in its own bucket, not in operating break-even.