GST Calculator
Two different questions: how much tax to add, and how much of an invoice is tax. Pick the mode.
Read the maths behind this tool: GST Calculation: Adding, Removing and Why Division Is Not Subtraction
Inclusive versus exclusive
A supplier quoting 100,000 plus GST invoices 118,000. A shop quoting 118,000 inclusive has 18,000 of GST inside — found by dividing, not subtracting.
Rates
The standard federal rate is 18%; provinces tax services separately with the same arithmetic.
Remove 18% from a total?
Divide by 1.18: 118,000 → 100,000 base.
GST same as sales tax?
Economically yes; the arithmetic is identical.