If I rent out a room in my HDB, is there any tax I need to pay to the government?

Yes, you need to pay two types of taxes to the government when you rent out a room in your HDB flat.

Any rent you receive from renting out a room must be declared as income and is subject to income tax. You calculate your taxable rental income by deducting allowable expenses from your gross rental rent. Allowable expenses include mortgage interest and maintenance costs. Alternatively, IRAS offers a simplified calculation where you can deduct a flat 15% of your gross rental income instead of calculating actual expenses.

Since you're renting out a room while still living in the flat, your HDB flat remains eligible for owner-occupier property tax rates, which are more favorable than non-owner-occupier rates. However, if you were to rent out the entire flat and move out, you would lose the owner-occupier rates and pay higher property tax at non-owner-occupier residential rates.

You also need to pay stamp duty on your written tenancy agreement within 14 days of signing. For room rentals, this is typically 0.4% of the total rent over the lease period (or market rent, whichever is higher), unless the average annual rent is below $1,000.

Make sure to declare your rental income in your annual Income Tax Return to IRAS to avoid penalties and compliance issues.