Relief for finance costs reduced to maximum allowable

I have input my tax calculation like the following : Foreign income after all allowance: £8358 Foreign savings £ 12140 therefore total income received £8358+£12140= £20498 minus personal allowance £12570 total income on which tax is due £20498-£12570=£7928 income tax charged afer allowance and relief in basic rate (£7928-£6000)x20%=£1928 x 20%= £385.6 minus Marriage allowane transfer £ 252 I had £8289 finance cost filled in 24.1 of SA106 however i saw £0x20% in the line (which i expect it should be £8289 x 20%= £1657.8 while i have the relief) minus Reflief for finance costs £8289 reduced to maximum allowable £0x20% and this made the final Income Tax due after tax reductions £385.6- £252= £133.6 only (which i expect it should be £385.6- £252- £1657.8) Can i know the reason i dont have the relief of finance cost of residential property?

Hi tungtax,
The relief is limited to your actual tax liability so in your case the tax due after deducting allowances and the marriage transfer is only £133.60.
The mortgage relief is therefore restricted to that.
You can then carry forward unused relief to later years.
Thank you. 

Can i know that what is the limitation of regarding mortgage relief? Is that base on the amount of mortgage interest amount or the tax due? However base on my testing on the system, when i input the same income in UK section but not oversea section, I can see the relief finally. I saw the post telling the same system fault in the community, when tax payers input the rental income and the mortgage interest expense in UK section but not oversea, the system shows the relief as expect. Could you please explain?

Hi tungtax,
Please refer to the SA106 help notes:
Use these notes to help you fill in the Foreign pages of your tax return
When completing the foreign pages to include overseas rental income, you can claim relief for residential finance costs by completing box 24.1 on page F5.
If this does not include the relief in the calculation please call our Self Assessment online technical support team. 
Technical support with HMRC online services
 Alternatively you can submit a paper tax return. 
Thank you.