Guides for small businesses and sellers
Clear answers to the questions behind our tools: what the fees are, how the tax works and how to price, with real numbers and the sources we checked. Each guide links to the free tool that does the sum for you.
Invoices & documents
GuideHow to write an invoice: what to include and how to get paid on time
An invoice is a request for payment that also serves as your record of the sale. This guide covers what to put on it, how to set terms customers actually follow, and a complete example with the numbers worked out.
GuidePurchase order vs invoice: what each one does
A purchase order is sent by the buyer before a sale to say what they want to buy. An invoice is sent by the seller after delivering to ask for payment. Here is how they fit together with packing slips and receipts.
GuideWhat a VAT invoice must include in the UK and EU
A VAT invoice has to show a set list of details, or your customer may not be able to reclaim the VAT. Here is that list for the UK and the EU, the shorter versions allowed for small sales, and a fully worked example.
Pricing & profit
GuideHow to calculate profit margin: gross, operating and net
Profit margin is the share of each dollar of sales you keep as profit. There are three versions, each answering a different question. Here is how to work out all three, with one set of numbers carried through.
GuideHow to calculate your break-even point
Your break-even point is the level of sales at which you stop losing money. Working it out takes three numbers and one division, and it turns a pile of costs into a sales target you can check against reality.
GuideHow to price a product: a step-by-step method
A good price covers every cost of making and selling the item, leaves a margin that pays for the rest of the business, and still makes sense to buyers. Here is how to get there in five steps.
GuideMarkup vs margin: the difference, the formulas and a conversion table
Markup is profit as a share of cost. Margin is profit as a share of the selling price. They describe the same sale with different numbers, and mixing them up is one of the easiest ways to underprice.
Online selling
GuideeBay vs Poshmark vs Mercari fees in 2026, plus Depop, Etsy and TikTok Shop
Each resale marketplace charges sellers in a different way, which makes headline percentages hard to compare. Here is the same US sale run through all six, with the arithmetic shown, and what changes on cheap items and promoted sales.
GuideEtsy fees explained: what Etsy charges on every sale in 2026
Etsy takes a listing fee, a 6.5% transaction fee and a payment processing fee on most sales, plus Offsite Ads and a regulatory operating fee in some cases. Here is what each one costs, what it is charged on, and how much a typical order loses to fees.
GuidePayPal, Stripe, Square and Venmo fees in 2026
The standard US rates for PayPal, Stripe, Square and Venmo, side by side, and what they cost on real payments. All figures are from each provider’s own pricing pages, checked in November 2026.
Marketing & ads
Sales tax & VAT
GuideHow to charge GST/HST in Canada: rates, registration and place of supply
In Canada, the sales tax you charge depends on where your customer is, not where you are. This guide covers when you must register, the rate for each province and territory, how to pick the right one, and what to put on your invoices.
GuideHow to pay quarterly estimated taxes on 1099 income
When no employer withholds tax from your pay, the IRS expects you to pay during the year in four installments. Here is who has to, how much to send, when it is due and how to pay.
GuideSales tax by state in 2026: every statewide rate
Every statewide sales tax rate for 2026 in one table, which states charge none, and how city and county taxes push the real rate higher. Use it as a starting point, then check the exact rate for the address you sell to.
GuideSelf-employment tax in 2026, explained with real numbers
Self-employment tax is the Social Security and Medicare tax for people who work for themselves. Here is how the 2026 rate, wage base and deduction work, with worked examples at three income levels.
Stock & inventory
GuideHow to calculate inventory turnover, and what to do with the answer
Inventory turnover tells you how many times you sell through your average stock in a period. Divide cost of goods sold by average inventory, then turn the result into days to see how long stock sits before it sells.
GuideReorder point and safety stock: formulas and examples
The reorder point is the stock level that tells you to place a new order so it arrives before you run out. Here is the formula, three ways to set safety stock, and how it fits with order quantity.
Pay & rates
GuideHow much does an employee cost? The real cost beyond salary
An employee costs more than their salary. In the US you also pay employer payroll taxes, unemployment taxes, insurance and any benefits you offer, which often adds 20% to 40% or more on top of pay depending on the benefits.
GuideHow to calculate overtime pay: federal rules, California and worked examples
Under federal law, non-exempt employees earn at least 1.5 times their regular rate for every hour over 40 in a workweek. Some states go further, and California also pays overtime by the day. Here is how to work it out correctly.
GuideHow to calculate your freelance hourly rate
A freelance rate has to pay for far more than your time on client work. Start from the income you need, add the costs an employer would normally cover, and divide by the hours you can really bill.
GuideHow to convert an hourly wage to an annual salary
Multiply your hourly rate by 2,080 to get a full-time annual salary. Here is where that number comes from, when it is wrong, and how to compare hourly and salaried offers fairly.
GuideHow to read a pay stub, line by line
A pay stub shows how your gross pay turns into the amount that reaches your bank account. Here is what each section means, the codes payroll systems use, and how to check the math.
Finance & tax
Guide12 financial ratios every small business owner should know
Twelve ratios, grouped into liquidity, debt, profitability and efficiency, tell you most of what a lender or buyer would want to know about a small business. Each takes two numbers from your balance sheet or income statement.
GuideLate payment fees: can you charge a late fee on an invoice?
You can usually charge a late fee or interest on an overdue business invoice if the customer agreed to it in advance. In the UK the law gives businesses a right to statutory interest and fixed compensation even without a contract term. In the US it comes down to your contract and your state’s law.