The equations
Original Price = Final Price ÷ (1 + Tax Rate ÷ 100). Tax Amount = Final Price − Original Price.
Forward check: Original × (1 + rate) should return your final within rounding.
Reverse Sales Tax Formula
Reverse sales tax is one division: Original = Total ÷ (1 + rate). Understanding why prevents the common mistake of multiplying by (1 − rate).
Live calculation
Reverse Sales Tax Formula
Reverse sales tax is one division: Original = Total ÷ (1 + rate). Understanding why prevents the common mistake of multiplying by (1 − rate).
Step 2 — Your breakdown
Original price (before tax)
$0.00
Tax amount
$0.00
Final price (verified)
$0.00
Explain calculation
We reverse the tax using the standard formula:
- Convert the rate to a decimal (e.g. 8.25% → 0.0825).
- Divide the final price by (1 + rate) to get the pre-tax amount.
- Subtract pre-tax from final to get the tax portion.
Enter a total and tax rate to see your breakdown.
Tool focus
Formula reference
Example rate
8.00%
Sample pre-tax
$100.23
Why divide by (1 + rate)?
If pre-tax price is P and rate is r, Final = P × (1 + r). Solving for P gives P = Final ÷ (1 + r). Multiplying by (1 − r) understates pre-tax and is incorrect.
Common use cases
- Spreadsheet template design
- Training new accounting staff
- Validating calculator output by hand
Tips for accurate calculations
- Store rate as a decimal (0.0825) in Excel to reduce typos.
- Round only at the end to match receipt cents.
Quick reference table
| Rate | Category | Examples |
|---|---|---|
| $100 @ 8% | Original | $92.59 pre-tax, $7.41 tax |
| $50 @ 6.25% | Original | $47.06 pre-tax, $2.94 tax |
| $1,200 @ 9.5% | Original | $1,095.89 pre-tax, $104.11 tax |
Worked reverse tax example
You paid $108.25 including 8.00% sales tax and need the merchandise amount for bookkeeping.
Convert rate: 8.00% ÷ 100 = 0.0800
Add 1: 1 + 0.0800 = 1.0800
Divide: $108.25 ÷ 1.0800 = $100.23
Tax portion: $108.25 − $100.23 = $8.02
Pre-tax: $100.23 | Tax: $8.02 | Total: $108.25
Compliance reminder
Reverse math is for splitting receipts and estimates—it does not replace filing obligations, nexus analysis, or professional tax advice. Confirm rates with your state revenue department or marketplace reports before remitting.
Frequently asked questions
No — that understates the pre-tax price. Always divide by (1 + rate), not multiply by (1 - rate).
Multiply your original by (1 + rate) — you should land back on the final price.
No—that understates pre-tax. Always divide by (1 + rate).