The tax relief that landlords of residential properties get for finance costs is being restricted to the basic rate of Income Tax. This is being phased in from 6 April 2017 and will be fully in place from 6 April 2020.
For the 2020 to 2021 tax year, the 100% phased in element of the loan cost is dealt with by a reduction in the basic rate allowance.
On SimpleTax under Property Expenses,
Select - MORTGAGE INTEREST & RELATED BANK CHARGES
Add the expenses category LOAN INTEREST PAID
Enter 100% of the interest paid at Box 44.
Please see the following link for further guidance: