Break-Even Calculator for Ecommerce Sellers

How to use this calculator

Why break-even matters for marketplace sellers

Break-even analysis answers the most important question before you invest in inventory: how many units must sell before this product pays for itself? Fixed costs — your initial stock buy, photography, software, storage — don't care how many units you sell. Each unit sold contributes its contribution margin (price minus variable cost) toward covering those fixed costs. Once cumulative contribution passes fixed costs, every additional unit is profit.

For marketplace sellers, the variable cost per unit should include everything taken per sale: product cost, inbound freight, the marketplace's referral/fulfillment fees, payment processing and ad spend. Use the Amazon FBA calculator or the eBay calculator to build an honest per-unit cost, then bring it here.

How the break-even calculation works

The engine is one number: contribution per unit — selling price minus variable cost per unit. Every sale pays that contribution towards your fixed costs, so break-even units = fixed costs ÷ contribution, and break-even revenue = break-even units × price. The units figure is rounded up, because you cannot sell 0.8 of a unit; the revenue line uses the exact figure, so it can sit a fraction below units × price.

Margin of safety then measures the cushion: (planned units − break-even units) ÷ planned units. A 10% margin of safety means a one-in-ten sales dip puts you underwater. The ACoS mode below runs the same arithmetic backwards for advertising: break-even ACoS is your contribution margin ratio — the share of each sale available to ads before profit hits zero — and max CPC = margin before ads × conversion rate. What the maths cannot do is judge your inputs: a variable cost that omits marketplace fees, returns or packaging produces a precise, wrong answer.

Worked example: a launch quarter, costed honestly

Invented round numbers \u2014 type them into the calculator and check us. A seller launches a home-organising product and treats the launch quarter's fixed costs as $3,600: tooling and photography for the first production run, software, and storage \u2014 costs that stay the same whether 10 units sell or 10,000. The product sells at $38. Variable cost per unit is $21.50: $13.00 product, $5.70 of marketplace fees, $2.80 of fulfilment and packaging. Contribution per unit: $38.00 \u2212 $21.50 = $16.50. Break-even: $3,600 \u00f7 $16.50 = 218.2 units, so 219 units \u2014 about $8,291 of revenue \u2014 before the launch has paid for itself.

Now the lever nobody plans for: advertising. Add $2.00 of ad spend to each unit's variable cost and contribution falls to $14.50, so break-even climbs to $3,600 \u00f7 $14.50 = 248.3 \u2014 249 units, thirty more sales for exactly the same quarter. Ads are not good or bad; they are a variable cost with a volume consequence, and this calculation is how you see the consequence before the spend happens.

Common break-even mistakes

Leaving marketplace fees out of variable costs. Referral and fulfilment fees are charged per order, so they are variable by definition. Treating them as "overhead" understates the break-even point.

Mixing one-off costs into monthly fixed costs. Launch photography or a trademark filing is not a monthly cost. Amortise one-offs separately or your break-even will look permanently out of reach.

Ignoring returns. If 5% of orders come back, your effective contribution is earned on 95 orders out of every 100 shipped. Return-heavy categories should model that.

Treating break-even as the goal. Break-even is the floor, not the target. Add the profit you actually want to fixed costs and recalculate — that is the volume your marketing plan has to deliver.

The FBA break-even price formula, in plain words

For an Amazon FBA product, the floor price has its own formula: break-even price = (landed unit cost + FBA fulfilment fee + other per-unit variable costs) ÷ (1 − referral fee rate).

In plain English: add up everything each unit costs you, then gross it up to cover the percentage Amazon takes off the top. The division is the step most sellers miss — they subtract the referral fee from the price instead, which understates the floor and quietly erases margin.

What belongs in each variable: landed unit cost is what one unit costs delivered and ready to sell — product, packaging, prep and its share of inbound freight. The fulfilment fee is Amazon’s per-unit pick, pack and ship charge for your product’s size tier and weight. Other per-unit variable costs are anything else that scales with each sale — a returns allowance, a per-unit ad budget, coupon costs. Keep fixed costs like the monthly Professional plan fee out of this formula; they do not change the per-unit floor. Confirm your category’s current referral rate and your product’s fulfilment fee in Seller Central before you calculate — fees change, so do not rely on a number memorised from any page, this one included.