Tools for E-commerce Sellers

Selling online — whether on Amazon, Etsy, Shopify, or your own site — comes down to a handful of numbers that are easy to get wrong if you're doing the math in your head. Four calculators cover the core ones.

What's your actual margin?

The Profit Margin Calculator works both directions: tell it your cost and price to find your margin and markup, or tell it your cost and a target margin to find the price you need to charge.

Profit Margin Calculator→

What do marketplace fees actually take?

Amazon, Etsy, eBay, and Shopify all take a cut differently, and their fee structures are tiered and change over time — so rather than hardcoding numbers that could go stale, the Marketplace Fee Calculator gives you an editable starting-point percentage and computes your real net profit once you enter your actual current rate.

Marketplace Fee Calculator→

Shipping and break-even

The Shipping Cost Estimator factors in dimensional weight (the box-size-based charge that catches a lot of sellers off guard), and the Break-Even Calculator tells you exactly how many units you need to sell before you're actually making money.

Shipping Cost Estimator→ Break-Even Calculator→

A worked example, start to finish

Say you sell a ceramic mug. Your landed cost is $12.00, packaging adds $0.80, you plan to charge $34.00, the marketplace takes 13% in total fees (an assumed figure; enter your real current rate), and shipping to the average customer costs $5.50.

• Fees: 13% of $34.00 is $4.42.
• Net profit per order: $34.00 - $12.00 - $0.80 - $4.42 - $5.50 = $11.28.
• Margin on the sale price: $11.28 / $34.00, about 33%.
• Break-even: if your monthly fixed costs (software, storage, samples) are $600, divide by $11.28 and you need roughly 54 orders a month before the mug line is in profit.

That last figure is the one sellers skip, and it often changes the decision. If you expect 30 orders a month, you have a pricing or cost problem, not a marketing problem.

Margin versus markup

These are different numbers and mixing them up is a classic mistake. With a $12 cost, a 40% markup gives a price of $16.80, but a 40% margin requires a price of $20.00, because margin is measured against the price you charge. When a supplier or a spreadsheet says "40%," confirm which one is meant. The Profit Margin Calculator shows both, so you can see the gap directly.

Shipping mistakes to avoid

• Quote shipping from a packed, measured box, not from the product's own dimensions. Dimensional weight charges the box size, so a light item in an oversized carton can cost more than a heavier item in a snug one.
• Re-check rates when you change packaging, even by an inch.
• Decide in advance whether shipping is built into the price or charged separately, and run the margin both ways. Free-shipping promotions that are not in the model quietly erase profit.

How often to rerun the numbers

Rerun the calculators whenever a supplier price, a marketplace fee schedule, or a carrier rate changes, and at least once a quarter. These tools give planning estimates based on the inputs you provide; they are not tax or accounting advice, so talk to a professional about sales tax, income tax and bookkeeping. They are part of the professional tools set, and heavier days are covered by a Day Pass or Monthly Pro on the pricing page, beyond the 10 trial usages a day.

See the full Small Business toolkit→