---
title: "Singapore Corporate Tax in a Non-SGD Functional Currency: The MAS Average Rate for Form C and Form C-S"
description: "Companies with a non-Singapore dollar functional currency prepare the tax computation in that currency but file Form C-S or Form C in Singapore dollars. IRAS requires the average of MAS month-end rates for the basis period. How it is computed, with worked figures."
canonical: https://allratestoday.com/blog/singapore-corporate-tax-functional-currency-exchange-rate/
source: AllRatesToday (https://allratestoday.com/) — Markdown mirror of the page above; index of all pages at https://allratestoday.com/llms.txt
generated: 2026-11-12T08:08:57.739Z
---

A Singapore company that keeps its books in US dollars does its tax computation in US dollars too. The Corporate Income Tax Return does not follow: every amount declared on Form C-S, Form C-S (Lite) or Form C is in Singapore dollars. IRAS prescribes the rate that bridges the two in its e-Tax Guide "Filing of Income Tax Computations in Functional Currencies other than Singapore Dollars" (third edition, 30 January 2026).

## The rule

Companies that prepare financial statements in a non-Singapore dollar functional currency prepare their tax computations in the same currency. The return must be completed in Singapore dollars, and the relevant non-Singapore dollar items are translated into Singapore dollar equivalents using the **average rate**.

IRAS defines that rate precisely: it is computed using the average of the month-end exchange rates for the financial period that constitutes the basis period, and the exchange rates supplied by the Monetary Authority of Singapore (MAS) should be used. The guide adds that otherwise the applicable rate will be the one the Comptroller considers reasonable.

## It is not the MAS monthly average

This is the detail that trips people up. MAS releases both a month-end value and an average for each month. The IRAS method uses the **month-end** values: add the month-end rates for each month of the basis period and divide by the number of months. For a twelve-month year that is twelve figures.

## Worked figures

Using the MAS daily table and taking the last rate of each month, the method gives these Singapore dollar rates:

| Basis period | USD | EUR | GBP | JPY (per 100) | CNY (per 100) | HKD (per 100) |
| --- | --- | --- | --- | --- | --- | --- |
| 1 January to 31 December 2025 | 1.3056 | 1.4753 | 1.7243 | 0.8728 | 18.21 | 16.75 |
| 1 April 2025 to 31 March 2026 | 1.2870 | 1.4942 | 1.7272 | 0.8539 | 18.18 | 16.49 |

For comparison, the average of every daily MAS rate in 2025 is S$1.3066 to the US dollar. The two methods differ in the fourth decimal place here, and the difference grows in a volatile year. The month-ends used for 2025 include 28 February, 28 March, 30 May, 29 August and 28 November, the last MAS tables of those months.

These figures are computed from the MAS data to illustrate the method. Compute your own from the MAS month-end rates for your basis period before filing.

## What the average rate is used for

- **Tax payable:** chargeable income in the functional currency, multiplied by the corporate income tax rate and by the average rate for the year of assessment.
- **Exemptions and caps** that the law states in Singapore dollars.
- **Group relief** between companies with different functional currencies.
- **Foreign tax credit**, and dividends or interest in Singapore dollars.

One exception: for a transfer of assets under section 24 between companies with different functional currencies, the guide uses the exchange rate prevailing at the date of sale.

## Changing functional currency

A company that changes from Singapore dollars to another functional currency makes an irrevocable election between two methods for the balances it carries across: the changeover rate, an average over the twelve months before the end of the last Singapore dollar accounting period, or the average rate method. The company also has to tell IRAS about a non-Singapore dollar functional currency through myTax Portal.

## Compute it from the API

```
# MAS daily USD rates for the basis period, as CSV
curl "https://allratestoday.com/api/v1/central-bank/mas/history?symbol=USD&from=2025-01-01&to=2025-12-31&format=csv" \
  -H "Authorization: Bearer YOUR_API_KEY"
```

Or from the assembled yearly CSV files, which hold the same MAS table per one unit of each currency:

```
import pandas as pd
url = "https://raw.githubusercontent.com/AllRates-Today/central-bank-exchange-rates/main/data/mas/history/2025.csv"
df = pd.read_csv(url, parse_dates=["date"])
usd = df[df["base"] == "USD"].set_index("date")["value"]
month_end = usd.resample("ME").last()      # last MAS table of each month
print(round(month_end.mean(), 4))          # 1.3056
```

History is on paid plans; a history request is counted as one call per currency per month of data. IRAS also offers an exchange rate search spreadsheet on its corporate tax pages.

This guide describes the rules as IRAS, Singapore Customs and MAS publish them, read on 11 November 2026. It is not tax advice; confirm the treatment for your facts with your tax agent.

## FAQ

### Which exchange rate does IRAS require for a non-SGD functional currency?

The average rate: the average of the month-end exchange rates for the basis period, using the rates supplied by the Monetary Authority of Singapore.

### Must Form C-S be filed in Singapore dollars?

Yes. The tax computation is prepared in the functional currency, but all amounts declared in the Corporate Income Tax Return must be in Singapore dollars.

### Is the IRAS average rate the same as the MAS monthly average?

No. IRAS uses the month-end rates: add the month-end rate for each month of the basis period and divide by the number of months.

### What was the average of MAS month-end USD rates for 2025?

Taking the last MAS table of each month in 2025, the average is S$1.3056 to the US dollar.

## MAS rates and live SGD on one key

Mid-market rates every 60 seconds and the official tables of [123 central banks and 6 tax authorities](https://allratestoday.com/central-bank-rates-api/institutions/), as JSON, CSV, XML or Excel. Paid plans from €4.99 a month.

 [See plans](https://allratestoday.com/pricing/)

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