Guides
The thinking behind the calculators: how each fee schedule really works, how to price for profit, what the loan numbers mean. Every guide is dated, cites its sources, and links to the calculator that does the arithmetic.
BMI and daily calories: what the numbers mean and where they break down
How BMI and total daily energy expenditure are calculated, what the categories and activity multipliers actually say, and the situations where each number is wrong.
eBay fees explained: what a sale really costs in 2026
The final value fee, the per-order fee, the $7,500 tier, promoted listings and the international fee, worked through on real sales so you can see where the money goes.
Etsy fees explained: listing, transaction, processing and Offsite Ads
Four separate fees add up to more than most sellers expect. What each one is, what it's charged on, and a worked example on a $35 order.
How to price a resale item so you actually make money
Work backwards from the profit you want, through fees, shipping and supplies, to the list price. A method, a worked example, and the three costs most sellers forget.
Mortgage payments explained: PITI, amortization and why the 15-year costs less
What's inside a monthly mortgage payment, how the level-payment formula works, why early payments are mostly interest, and what a shorter term or an extra $100 a month actually does.
PayPal goods and services vs friends and family: fees, protection and tax
What each payment type costs, who is protected, why asking a buyer to "send as friends" is a bad trade, and how to price so the fee doesn't come out of you.
Poshmark vs Mercari vs Depop: which takes the least from a sale
Three clothing marketplaces, three completely different fee structures. The same item sold on each, at $12, $30 and $80, so you can see which wins at which price.
Taxes for resellers and freelancers: the 1099-K, Schedule C and quarterly payments
When selling online becomes taxable income, what the 1099-K does and doesn't mean, how self-employment tax is calculated, and how much to set aside each quarter.
Sales tax for online sellers: marketplace facilitator laws explained
Who collects sales tax when you sell on eBay, Etsy or Mercari, when you have to collect it yourself, what nexus means, and how to back tax out of a receipt.
Shipping for resellers: how to stop losing money on labels
Why the label is usually your second-biggest cost, how weight tiers and zones work, what "free shipping" really costs, and how to charge for it without being undercut.