Reverse GST Calculator
Extract the GST from a GST-inclusive amount. Free reverse GST calculator to find the base value and tax from a total at 5%, 12%, 18% or 28%.
Frequently asked
- How do I remove GST from a total?
- Divide the total by (1 + rate). For 18%, base = total ÷ 1.18. The GST is the total minus that base.
- Why isn’t it just total minus 18%?
- Because the 18% was added to the base, not the total. Subtracting 18% of the total over-removes the tax. The correct base is total × 100 ÷ 118.
On a Retainer invoice you enter the base and GST is added correctly — you never have to work backwards from a total. Try Retainer free