I’ve noticed that reverse tax calculations are easy to get wrong, especially when you only have the final price from a receipt or invoice.

For example, if an item costs $550 including 10% tax, simply taking 10% off $550 doesn't give the correct pre-tax price.

The correct calculation is:

$550 ÷ 1.10 = $500

So the breakdown is:

Before tax: $500
Tax: $50
Final price: $550

The reason is that the 10% tax was calculated from the original $500, not from the final $550.

For anyone who deals with tax-inclusive prices regularly, I found Calculate Reverse Tax useful for checking the pre-tax amount and included tax without repeating the formula manually.

It can be handy for checking invoices, receipts, product prices, expenses, or simply verifying a calculation before using the numbers elsewhere.

One thing I always recommend is checking that the amount is actually tax-inclusive and that you're using the correct tax rate for the transaction.

How do you normally calculate reverse tax—manually or with a calculator?