How to calculate 10% service charge and 7% GST?

If you frequently go out for meals with friends at restaurants (in before COVID circuit breaker stay-home joke), you’ll be familiar with the addition of 10% service charge and 7% Goods and Services Tax (GST) to your bill.

Most people do not realise that the service charge is also taxable and will typically multiply the cost by 1.17. However, the correct multiplier is actually 1.177 instead.

Here’s a simple breakdown:

GST (7%): Cost x 1.07
Service Charge (10%): Cost x 1.1
GST and Service Charge: Cost x 1.177

So simple!