Question 1

Adding tax

Accepted Answer

To add tax, multiply the net price by one plus the rate over 100. $100 at 8.5% becomes $100 × 1.085 = $108.50, of which $8.50 is tax. This is what you do when quoting a price before tax is applied.

Question 2

Removing tax

Accepted Answer

To strip tax from an inclusive total, divide by one plus the rate — don’t just subtract the percentage. $108.50 ÷ 1.085 = $100 net, not $108.50 − 8.5%, which would be wrong. The calculator does this correctly in “remove” mode.

Question 3

Sales tax vs VAT

Accepted Answer

Sales tax is usually added at the till and shown separately; VAT and GST are typically baked into the displayed price. The maths is identical — what differs is whether the figure you start with already includes the tax.

Question 4

Common mistakes

Accepted Answer

Subtracting the percentage to remove tax (it overshoots); applying the rate twice; and mixing inclusive and exclusive prices in the same total.

增值稅計算機 — 加稅或去稅

加稅

去稅

銷售稅 vs 增值稅

常見錯誤

唔會做嘅嘢