When buying BTO under deferred income assessment, what happens if my income exceeds 14k?

I would like to answer my own question. The eligibility for BTO (combined income <14k) is assessed when you sign the papers for your house now. HDB considers your income for the past three months. If one falls under defered income assessment, the assessment of income will be done 3 months before key collection. This is only to assess how much CPF grants are given. All this was explained to me when I called the hdb hotline.

With a household income exceeding $14k, you won't be eligible for CPF housing grants. But if your household income in four years' time will exceed $14k - I doubt you'll be eligible for much grants now. The most "lucrative grant" - the EHG - requires a household income ceiling of $9k (for which the amount of grant is only $5k).

But don't worry, it's a happy problem. Better to have more income and no grant than to have a lot of grants due to a low household income.

Have you tried the HDB website's eligibility check?