Software: MoneyWorks accounting software
GST (Goods and Services Tax) applies when you supply goods and services locally, even if you invoiced the customer in foreign currency. Besides, for the foreign currency invoices, you are required to show the total amount payable excluding tax, the GST rate, GST amount, and the total amount including tax separately in Singapore Dollars equivalent.
The Transaction.ExchangeRate field shows the exchange rate used of a posted Sales Invoice transaction. For unposted Sales Invoice transaction, you may use a If ( ) together with a CurrencyConvert (amount, FromCurrency, ToCurrency [, periodOrDate]) function to pull out the exchange rate used.
The exchange rate formula used of an unposted Sales Invoice:
if (Transaction.ExchangeRate = 0, CurrencyConvert (1, BaseCurrency, Currency, TransDate), ExchangeRate)
Use the above exchange rate formula to convert the amount excluding tax, GST amount, and amount including tax which is in a foreign currency, separately into Singapore Dollars equivalent.
To convert the GST amount of US Dollars 74.68 into Singapore Dollars equivalent at the exchange rate ratio of 1SGD : 0.7143USD, enter the below formula in the Calculation Box of a Calculation Box Tool.
Transaction.TaxAmount / if (Transaction.ExchangeRate = 0, CurrencyConvert (1, BaseCurrency, Currency, TransDate), ExchangeRate)
This will give a result of 104.55 (that is 74.68/0.7143).
Reference: MoneyWorks v7 User Guide, Page G-379 — Forms Designer and Page G-416 — Calculating and things.