Indirect tax is a cash-flow problem, not an accounting one
Sales tax, VAT and GST are not your money. You collect them on behalf of a tax authority and hand them over at the end of the period. The businesses that get into trouble are rarely the ones that calculated a rate wrongly. They are the ones that treated collected tax as working capital, spent it, and then had to find the cash at filing time. Getting the number right at the point of quoting is the first step in never being surprised by a return.
Why there is no single US sales tax rate
The United States has no federal sales tax. What a customer pays is the sum of a state rate, often a county rate, sometimes a city rate, and occasionally a special district rate for transit or stadium funding. Most states are destination-based, which means the rate is set by where the buyer takes delivery, not where you are. That is why the calculator asks for four separate components instead of pretending a single number exists.
VAT and GST run on the same logic
Both are value-added taxes: you charge output tax on sales, reclaim input tax on purchases, and remit the difference. The UK applies a standard rate of 20%, a reduced rate of 5% and a zero rate, with registration required once taxable turnover passes the threshold. India runs slabs of 0, 5, 12, 18 and 28%, split into CGST and SGST for supplies inside a state and charged as a single IGST across state lines. The split changes who receives the revenue. It never changes what the customer pays.
Adding tax and removing tax are different sums
Adding 20% VAT to 100 gives 120. Removing 20% VAT from 120 does not mean subtracting 20% of 120. You divide by 1.20, which returns 100 and a 20 tax element. Subtracting 20% would have given 96 and lost you four pounds on every transaction. Every tool here handles both directions correctly, and the VAT calculator also shows the VAT fraction so you can check the arithmetic by hand.
Self-employment tax catches new freelancers out
When you were an employee, your employer quietly paid half of Social Security and Medicare. Self-employed, you pay both halves: 15.3% on 92.35% of net earnings, with the Social Security portion capped at an annual wage base and Medicare uncapped. Half of it is deductible against income tax, which softens the blow, but the cash still has to be set aside quarterly. The calculator shows the full breakdown so nothing arrives as a surprise in April.
Rates you enter, not rates we guess
Every rate field is editable and pre-filled with a sensible default. That is a deliberate design choice. A tool that hardcodes last year's wage base or a single state rate quietly produces wrong answers forever. Check the current figure against the primary source linked at the bottom of each tool page, enter it once, and the maths will be right.