Field help:

Enter the total amount of foreign income that is not subject to German income tax. If you did not have any foreign income, enter "0" here.

If applying for unlimited tax liability or applying for the personal and family-related tax benefits, the amount of foreign income earned during the time abroad which was not subject to German income tax must be checked.

This income is taken into account when determining your tax rate (so-called "progression clause (Progressionsvorbehalt)". This means that the income is used as the basis for stipulating the rate of tax you need to pay on your taxable income.

The conversion of income in foreign currency must be done on a monthly basis using the Euro reference rate from the European Central Bank. However, it is not objectionable if wage payments received in a foreign currency are converted on the basis of an annual conversion rate - determined from the VAT reference rates published monthly, rounded down to the nearest 50 cents. (Ministry of Finance (BMF) letter dated 14.12.2014)

Here is an overview of the annual conversion rates for the key foreign currencies.