The reseller money picture, and which tool solves which question
Selling online looks simple from the outside: list an item, ship it when it sells, keep the difference. The money picture underneath is not simple, and it is not the same on any two platforms. What you actually keep from a sale depends on the platform's fees, on what you paid to source and ship the item, and, once your volume grows, on how the sale is taxed. This page lays out that whole picture in order, then points you at the tool in the family that answers each specific question with your own numbers.
Fees are the first thing that eats your sale
Before tax ever enters the conversation, the platform takes its cut, and every marketplace slices it differently. eBay charges a percentage final value fee on the total the buyer pays, including shipping and tax, plus a small fixed fee per order. Poshmark uses a two-tier commission: a flat fee on low-priced items and a percentage once you cross a price line, with a separate flat shipping fee the buyer usually pays. Mercari has changed its structure more than once, moving fees between the seller and the buyer over time. The practical result is that the same $40 item nets you a different amount on each platform, and a fee quoted as a single percentage almost never captures the fixed per-order pieces that matter most on cheaper items. If you only remember one thing about fees, remember that the headline percentage is not the whole fee.
This is why comparing platforms is harder than it looks. A percentage on one marketplace and a flat fee on another cannot be lined up side by side without running an actual sale through each. On a $12 item, a flat fee can cost you a quarter of the sale, while the same item priced at $60 pays a much friendlier effective rate elsewhere. The only reliable way to know where a given item nets the most is to price it against each platform's real fee structure, item by item, rather than trusting a single "best platform" rule of thumb.
Fees also change. eBay adjusted its final value fee structure in February 2026; Poshmark and Mercari have each revised their terms in recent years. That churn is exactly why a dated fee table beats a blog post that was accurate the year it was written and silently wrong ever since. The pillar guide on this hub keeps the current numbers with the date they were verified, so you can see how fresh the figure is before you rely on it.
The 1099-K, and why a form is not a tax bill
The second half of the money picture is tax, and the piece that causes the most panic is the Form 1099-K. A 1099-K is an information return: a marketplace or payment app files it with the IRS to report the gross payments it processed for you, and sends you a copy. Whether you get one depends on a reporting threshold that changed direction three times in four years. For 2024 the rule was $5,000 in gross payments with no transaction minimum. For 2025 and 2026 the old standard is back, restored permanently by the One Big Beautiful Bill Act: a platform issues a form only if you cross both $20,000 in gross payments and more than 200 transactions on that platform.
The single most important point is that the form does not decide whether you owe tax. Profit from selling is taxable whether or not any form is issued, and receiving a 1099-K does not mean you owe tax on the whole gross figure it shows, because you subtract what your items cost and your selling expenses first. The threshold decides paperwork; your profit decides tax. Getting that order right saves a lot of unnecessary worry, and a fair amount of overpaying.
Which question, which tool
Reseller Math is built around the idea that each of these questions deserves a focused tool rather than a wall of prose. If your worry is the tax side, whether a form is coming, whether your selling counts as a hobby or a business, and what self-employment tax a profit might carry, the 1099-K Checker applies the correct year's rule to your own totals and shows its work.
If you sell on Poshmark and negotiate, the hard part is working backwards: you know what you want to keep, but the offer-to-likers ladder and the commission sit between you and that number. The Poshmark Offer Calculator reverses the math, starting from your target take-home and telling you what to offer so the fees and shipping still leave you where you want to be.
If you run eBay Promoted Listings, the question is where the ad spend stops paying for itself. Push the ad rate too high and a promoted sale earns you less than an organic one would have. The eBay Promoted Listings Breakeven tool finds the ad rate where a promoted sale stops making you money, and it includes a companion max-buy-price calculator so you can source inventory that still has room for profit after fees.
Freshness is the whole point
The reason these tools exist as a maintained family, rather than a single dated article, is that the inputs move. Fee percentages get revised, per-order fees get added, and tax thresholds get rewritten by legislation. Every fee table and threshold in the family lives in a dated data module, and that date is shown next to the numbers, so you can always judge how current the answer is. When a platform or the IRS announces a change, the figure and its date are updated together. Start from the question you actually have, pick the tool that answers it, and check the date on the number before you build a decision on it.