I live off my investment income that has been previously taxed in my home country: regional capital dividends, interest, capital gains. Will they attribute the funds, between capital dividends and capital gains?

It is up to you to go through these funds and calculate what are the capital gains, dividends and interests on those assets. You need to keep clear records for each asset type. Remember it is up to the tax payer to prove what the source of remittance is from and how they are to be taxed.

Read our A Guide to Understanding Assessable Foreign-Sourced Income in Thailand to learn more.