Quick answer
If you’re UK resident, rent from overseas property counts towards your MTD qualifying income, before expenses. Your overseas lets are a separate property business from any UK lets, so they need their own quarterly updates.
It counts towards the threshold
Someone with £20,000 of rent from a UK flat and £15,000 from an apartment in Portugal has £35,000 of qualifying income.
A separate property business
UK property and overseas property are reported separately. If you have both, you send quarterly updates for each.
Foreign tax
If you’ve paid tax abroad on the rent, you may be able to claim Foreign Tax Credit Relief in your final declaration.
Living outside the UK yourself? See MTD if you live outside the UK.