Break-even Calculator Ecommerce#

Calculate the real no-loss line before deciding whether to launch harder, discount harder, or scale paid traffic.

This is not a generic margin calculator. It separates variable from fixed costs, models real ecommerce unit economics (returns, payment fees, platform takes), and translates math into actionable launch/hold/scale decisions.

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Quick Reference#

DecisionKey MetricGreenYellowRedLaunch viabilityContribution margin %> 40%20–40%< 20%Ad scaling roomBreak-even CPACPA < 60% of CMCPA 60–90% of CMCPA > 90% of CMDiscount safetyMargin after discount> 25% CM remaining10–25% CM remaining< 10% CM remainingFree shippingMargin absorptionShipping < 30% of CMShipping 30–50% of CMShipping > 50% of CMScale readinessBreak-even units/mo< 50% of current vol50–80% of current vol> 80% of current vol

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Solves#

Ecommerce operators lose money not because they can't calculate margins, but because:

• They use gross margin when they should use contribution margin
• Platform fees, payment processing, returns, and packaging get excluded from "cost"
• Ad scaling decisions are made on ROAS without knowing actual break-even ROAS
• Discount and free-shipping policies are set without modeling margin impact
• "Profitable" products turn unprofitable at scale because fixed costs aren't allocated
• Teams confuse revenue growth with profit growth

Goal: Give operators a clear, reviewable break-even model that supports real decisions — not just a number.

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Use when#

• You need a break-even view before launching or scaling a product
• A team is changing price, discount, bundle, or free-shipping policy
• Paid acquisition is growing but true profitability is unclear
• Margin pressure is increasing and you need a decision baseline fast
• Evaluating whether to run a promotion, flash sale, or bundle offer
• Comparing profitability across SKUs, channels, or fulfillment methods
• Building a case for price changes or cost reductions

Do not use when#

• You need full accounting, tax treatment, or cash-flow modeling
• Core inputs are missing and nobody can provide reasonable assumptions
• The task is valuation, forecasting, or board-level finance reporting
• You only want gross revenue math without cost realism
• Legal or compliance-sensitive financial reporting is required

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Inputs#

Gather these inputs — mark any assumptions explicitly:

Revenue side:

• Selling price (or price range if testing)
• Average order value (AOV) if bundling
• Expected discount % or coupon structure

Variable costs per unit:

• COGS / unit cost (landed cost including freight to warehouse)
• Shipping to customer (outbound)
• Packaging & pick-pack-ship labor
• Payment processing fees (typically 2.5–3.5%)
• Platform/marketplace fees (e.g., Amazon 15%, Shopify Payments 2.9%)
• Return/refund rate and cost per return

Acquisition costs:

• Ad spend or budget
• Target or actual CPA (cost per acquisition)
• Target or actual ROAS
• Organic vs paid traffic mix if known

Fixed costs (if relevant):

• Monthly overhead (warehouse, tools, staff)
• Subscription/platform fees
• Content/creative production costs

See references/cost-breakdown-guide.md for detailed cost taxonomy.

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Workflow#

1. Separate variable costs from fixed costs#

This is the most common error. Be explicit about what scales with volume and what doesn't.

Variable (per-unit):

• COGS, shipping, packaging, payment fees, platform fees, returns

Fixed (per-period):

• Rent, salaries, SaaS tools, insurance, loan payments

Semi-variable (step functions):

• Warehouse staff (fixed per shift, but add shifts at volume thresholds)
• 3PL fees (often tiered)

Use the cost classification in references/cost-breakdown-guide.md to ensure nothing is missed.

2. Calculate contribution margin#

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Contribution Margin (CM) = Selling Price - Total Variable Costs per Unit
CM% = CM / Selling Price × 100

Include ALL variable costs:

• COGS
• Outbound shipping (if seller-paid)
• Packaging + pick-pack
• Payment processing (% of selling price)
• Platform/marketplace fees (% of selling price)
• Return cost allocation = (return rate × cost per return)

3. Calculate break-even points#

Break-even units (with fixed costs):

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BE Units = Fixed Costs / CM per unit

Break-even CPA:

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BE CPA = CM per unit (before ad spend)

This is the maximum you can pay to acquire a customer and still break even on first order.

Break-even ROAS:

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BE ROAS = Selling Price / (Selling Price - CM + CPA target)

Or more simply:

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BE ROAS = 1 / (CM% before ad spend)

4. Run sensitivity analysis#

Model how the break-even shifts when key inputs change. Focus on the variables the team can actually control:

VariableTest rangeImpact onSelling price±10–20%CM, BE units, BE ROASCOGS±5–15%CM, BE unitsAd CPA±20–50%Profitability, scale roomReturn rate±3–10ppCM, effective marginDiscount depth10/15/20/25% offCM, BE units, BE ROASShipping policyPaid vs free vs thresholdCM, conversion rate

Use references/sensitivity-template.md for structured output.

5. Translate to decisions#

Don't just output numbers. Frame results as decisions:

ResultDecision framingCM > 40%, BE CPA has roomScale: Increase ad spend, test new channelsCM 20–40%, tight CPA roomOptimize: Reduce COGS, improve conversion, test pricingCM < 20%Hold: Don't scale until unit economics improveDiscount breaks BEDon't discount: Use value-adds instead of % offFree shipping kills marginSet threshold: Offer free shipping above $X AOVHigh return rate crushing CMFix product/listing: Returns are a product/expectation problem

6. Quality-check the model#

Before presenting results, verify with assets/model-checklist.md:

• Are all variable costs included?
• Are assumptions labeled with confidence levels?
• Does the model account for returns?
• Is payment processing calculated on selling price (not COGS)?
• Are platform fees applied correctly?

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Output#

Return a structured analysis package (see references/output-template.md):

1. Assumptions table
   • Every input listed with source (actual data vs estimate vs industry benchmark)
   • Confidence flag: ✅ confirmed / ⚠️ estimated / ❓ assumed
2. Unit economics breakdown
   • Revenue per unit → all variable costs → contribution margin
   • Show each cost line, not just totals
3. Break-even results
   • Break-even units per month
   • Break-even CPA
   • Break-even ROAS
   • Current margin vs break-even margin
4. Sensitivity analysis
   • 2–3 scenarios showing how key variables shift break-even
   • Highlight which variable has the strongest impact
5. Decision recommendation
   • Launch / Hold / Scale / Optimize
   • Specific actions based on the numbers
   • Risk flags (e.g., "margin too thin for discounting")

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Quality bar#

Strong output should:

• Show all math explicitly — no black boxes
• Keep variable and fixed costs clearly separated
• Include return/refund impact (most calculators ignore this)
• Label every assumption with confidence level
• Frame results as decisions, not just numbers
• Help teams avoid "fake-profit" decisions

What "better" looks like#

Better output goes beyond "your break-even is X units." It helps decide:

• Whether the offer is viable at current costs
• How much ad spend room exists before break-even
• Whether discounting breaks the model
• Which cost lever matters most (COGS? Shipping? Returns?)
• Whether the business is near scale-ready or still too fragile
• What would need to change to make the unit economics work

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Examples#

Example 1: DTC skincare product#

Inputs:

• Selling price: $45
• COGS: $8.50
• Shipping: $5.50
• Packaging: $2.00
• Payment processing (3%): $1.35
• Platform fees: $0 (own Shopify store)
• Return rate: 8%, cost per return: $7

Calculation:

• Return cost allocation: 8% × $7 = $0.56/unit
• Total variable cost: $17.91
• Contribution margin: $27.09 (60.2%)
• Break-even CPA: $27.09
• If actual CPA is $18 → $9.09 profit per order → Scale

Example 2: Amazon marketplace electronics#

Inputs:

• Selling price: $29.99
• COGS: $11.00
• FBA fees: $5.50
• Amazon referral (15%): $4.50
• Return rate: 12%, cost per return: $9

Calculation:

• Return cost allocation: 12% × $9 = $1.08/unit
• Total variable cost: $22.08
• Contribution margin: $7.91 (26.4%)
• Break-even CPA: $7.91
• If PPC CPA is $6.50 → only $1.41 profit per order → Optimize before scaling

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Common mistakes#

1. Forgetting payment processing fees — 2.5–3.5% of every sale adds up fast
2. Ignoring return costs — A 10% return rate with $8 return cost = $0.80/unit drag
3. Using gross margin instead of contribution margin — Gross margin excludes shipping, fees, returns
4. Not modeling discounts through — A 20% discount on a 30% margin product leaves only 10% margin
5. Treating CPA as fixed — CPA rises as you scale (diminishing returns on ad spend)

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Resources#

• references/output-template.md — Structured output format
• references/cost-breakdown-guide.md — Comprehensive cost taxonomy for ecommerce
• references/sensitivity-template.md — Sensitivity analysis framework
• assets/model-checklist.md — Pre-delivery quality checklist