Most vendors think about sales tax forward: start with a price, apply the rate, get the total. But sometimes you need to go the other direction — you have the tax collected and need to find the original sale amount. That's reverse sales tax.
When Do You Actually Need This?
A few common situations:
- Your square reader shows "tax collected: $4.20" at the end of the day and you need to know what sales figure that represents
- You priced everything tax-inclusive (the tag says $25, that's what the customer pays) and now you need to separate the tax for your books
- You collected a round amount and want to verify the tax component for a refund
- An accountant asks for your pre-tax revenue and you only have totals
The Math
Standard forward calculation: pre-tax price × (1 + rate) = total
Reverse calculation: total ÷ (1 + rate) = pre-tax price
So if you charged $26.75 for an item in a 7% tax state:
$26.75 ÷ 1.07 = $25.00 pre-tax
And the tax was $1.75.
Or if you know you collected $4.20 in tax at 6%:
$4.20 ÷ 0.06 = $70.00 pre-tax sale
Why It's Tricky
The mistake most people make is just subtracting the rate from the total. If you have a $107 sale at 7%, subtracting 7% gives you $99.51 — but the correct pre-tax amount is $100.00. The difference is small on one transaction but adds up across a day of sales, and it'll cause problems when you reconcile your books.
The correct denominator is always 1 + (rate / 100), not just applying the percentage to the total.
Use the Calculator, Skip the Math
reversesalestax.us does all of this instantly. Enter the tax amount you collected, select your state, and it returns the pre-tax sale price and total. It also handles the edge case where a state has no sales tax — no more trying to remember whether Montana charges tax (it doesn't).
Tax-Inclusive Pricing: A Strategy Worth Knowing
Some vendors choose to price their goods tax-inclusive — the sticker price is the final price the customer pays, and tax is already baked in. This makes for a smoother transaction (no mental math at the register) but means you need to extract the tax component later for your records.
If you price this way, reverse sales tax isn't just occasionally useful — it's part of your regular bookkeeping workflow. Run it after every show to get your clean pre-tax revenue figure.
Bottom Line
Reverse sales tax is the backwards version of the calculation you already know. When you have the tax collected and need the original sale, divide by (1 + rate). When you have the total and need the pre-tax price, same formula. Or just use reversesalestax.us and skip the division entirely.