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To reverse calculate GST, divide the total by 1.05. A $525 price with 5% GST included was $500 before tax, and $25 of it was GST. Multiplying $525 by 5% gives $26.25, which is wrong, because the tax was charged on the smaller pre-tax price. In HST provinces, divide by 1.13, 1.14 or 1.15.
How do I take GST out of a price?
Add the tax rate to 1 and divide the total by that number. With 5% GST the divisor is 1.05. For a total of $525, $525 divided by 1.05 is $500. The tax is the total minus the pre-tax price: $25.
There’s a shortcut if you only want the tax. Multiply the total by 5 and divide by 105. For $525 that’s $2,625 divided by 105, which is $25. The same trick works for any rate: 13 over 113 for Ontario HST, 15 over 115 where HST is 15%.
The reverse tax calculator does this for any province, and it shows the split so you can copy the numbers into an invoice or an expense report. If you’re going forward instead, from a pre-tax price to a total, use the GST/HST calculator.
Which divisor fits my province?
The place of supply sets the rate, so look at where the sale is made. The CRA’s page on charging and collecting the GST/HST says the rate depends on the place of supply, and it confirms Nova Scotia’s 14% rate. Ontario’s HST is 13%, and the other participating provinces charge 15%. Provinces without HST charge 5% GST on its own.
| Rate charged | Divisor | Example total | Before tax | Tax inside |
|---|---|---|---|---|
| 5% GST (for example Alberta) | 1.05 | $525.00 | $500.00 | $25.00 |
| 13% HST (Ontario) | 1.13 | $1,130.00 | $1,000.00 | $130.00 |
| 14% HST (Nova Scotia since 1 April 2025) | 1.14 | $1,140.00 | $1,000.00 | $140.00 |
| 15% HST (for example New Brunswick) | 1.15 | $1,150.00 | $1,000.00 | $150.00 |
| 12% in BC, GST plus PST | 1.12 | $112.00 | $100.00 | $12.00 |
Say a Halifax contractor hands you an invoice for $228 all in. Divide by 1.14 and the work was $200, with $28 of HST. Use 1.15 by habit and you’d get $198.26, which is off by a few bucks and will bug your accountant at tax time.
What about cents that don’t divide evenly?
Most real totals don’t land on round numbers. Take $84.75 paid in New Brunswick at 15%. Divide by 1.15 and you get $73.70, with $11.06 of HST. But $73.70 plus $11.06 is $84.76, one cent over what you paid.
That’s rounding, and it’s normal. Each figure is rounded by itself, and sometimes they disagree by a cent. Keep the total you actually paid as the anchor, and let the tax figure absorb the penny if your books need to balance.
When should I back out the tax?
Mostly when you’ve got a receipt and need the tax part. Businesses that are registered for GST/HST do this when they claim input tax credits, and some do it on old invoices where only the total was recorded. Small suppliers, those at or below $30,000 of taxable sales in a single calendar quarter and over the last four consecutive quarters, aren’t required to register, so they wouldn’t charge it in the first place.
Also, and this is where people trip, not every receipt has GST in it. Basic groceries are zero-rated, which means 0% GST/HST, in every province and territory. Dividing a grocery total by 1.05 would invent a tax that was never charged.
Mistakes to avoid in a reverse calculation
Multiplying instead of dividing is the big one.
Using 5% in an HST province is another, and so is using 12% in BC on an item that was exempt from PST, where the receipt only carried 5%. Both make the pre-tax price look wrong by a few dollars on a few hundred, which is enough to fail a reconciliation.
That last one affects our own BC setting. The GST and PST calculator applies the full 12% to whatever you enter, so for a PST-exempt item divide by 1.05 yourself. In Quebec, the QST has its own formula, handled by the GST and QST calculator.
Can I reverse a total that mixes taxed and untaxed items?
Not in one step. If a $60 receipt has $20 of zero-rated groceries and $40 of taxable items at 5% GST, the $20 has no tax inside. Only the $40 gets divided: $40 divided by 1.05 is $38.10, so the GST is $1.90. The split has to follow the lines on the receipt, not the grand total.
What does a reverse calculation look like on a real invoice?
An Ontario supplier bills you $226.00 all in. Divide by 1.13 and the work cost $200.00, with $26.00 of HST inside. Check it forward: $200.00 times 1.13 is $226.00. That round trip is the quickest way to catch a slip before the number goes into your books.
If you claim input tax credits, the $26.00 is the amount that matters, and keep the invoice with your records. Claiming input tax credits needs supporting documents, and the CRA says business records must be kept for six years.
Are the divisors the same in 2026 and 2027?
As of November 2026 the CRA's rate table lists 5% GST, 13% HST in Ontario, 14% in Nova Scotia and 15% in New Brunswick, Newfoundland and Labrador and Prince Edward Island. We found no announced change to those rates for 2027, but provinces set their own rates in budgets, so check the table again before you code a new divisor into your invoicing system. Quebec's QST and the PST in British Columbia, Saskatchewan and Manitoba are separate taxes and work differently.
If you are comparing places rather than backing out one receipt, see which province has the lowest sales tax. To read each line on a receipt, the page on reading GST and HST on a receipt goes through it, and the guide to GST, HST, PST and QST covers who charges what.
What this page is based on
Rates come from the CRA table of GST/HST rates by province and its page on which rate to charge, which confirm Nova Scotia at 14% since 1 April 2025 and 0% on basic groceries. The $30,000 small supplier test comes from CRA registration guidance. All checked in November 2026. The CRA table does not split HST into federal and provincial parts for every province, so we do not give one. The worked examples were computed with code.
Frequently asked questions
How do I calculate GST backwards?
Divide the total by 1 plus the rate. At 5% GST, divide by 1.05, which gives the price before tax, then subtract that from the total to get the GST. For $525 the pre-tax price is $500 and the GST is $25. The same method works for any HST rate.
Why isn't the tax 5% of the total?
The 5% was charged on the price before tax, which is smaller than the total you paid. Taking 5% of $525 gives $26.25, but the real GST was $25. The error grows with the size of the bill, so always divide instead of multiplying.
What divisor do I use in Ontario?
Use 1.13, because Ontario HST is 13% on the CRA rate table. A total of $226 divides to $200.00 before tax with $26.00 of HST. Use 1.14 in Nova Scotia and 1.15 in New Brunswick, Newfoundland and Labrador and Prince Edward Island.
Why is my answer a cent off?
Each figure is rounded to the cent on its own, so the two parts can differ from the total by one cent. Treat the amount you paid as fixed and let the tax figure absorb the penny, so your books still match the bank statement.
Does this work for groceries?
No. Basic groceries are zero-rated, so the rate is 0% GST/HST in every province and territory, according to the CRA, and no tax sits inside the price. Dividing a grocery total by 1.05 would invent a tax that was never charged. Check each line of the receipt first.
- GST, HST, PST and QST explained for every province
Which GST, HST, PST or QST applies where you shop or sell in Canada, the 2026 rates for every province, who must register and how to add or remove tax