These are two very different numbers, and mixing them up is one of the easiest ways to get caught off guard. Construction-loan interest is a temporary payment during the build. The permanent mortgage payment is the long-term payment your life has to carry after the home is done.
Construction phase
During the build
interest-only payment on the drawn balance
Long-term phase
After completion
principal and interest payment on the full mortgage
Common surprise
Often higher
the finished payment than people expect if they only watched the build phase
What you pay during construction
During the build, construction loans are usually interest-only. You are paying interest on the amount that has actually been drawn, not the full future mortgage balance. Early in the project that number may feel manageable because only part of the loan is in use.
What you pay after the build is complete
Once construction ends, the loan generally converts into a permanent mortgage. At that point the payment is based on the full loan amount, the permanent rate, and the amortization term. That number includes principal as well as interest, which is why it can be materially higher than the construction-phase payment people got used to seeing.
If the project cost increased during construction, the permanent payment often increases too. That is why it is risky to judge affordability by the build-phase interest payment alone.
Why the gap surprises people
- The construction payment is based on a partial balance for much of the build.
- The permanent payment is based on the full long-term loan.
- Principal repayment begins after conversion.
- Change orders and budget creep can increase the final amount financed.
What to watch before conversion
- The latest projected total project cost
- How much contingency has been consumed
- Whether the draw schedule is increasing the expected final loan amount
- What the finished-home payment looks like at a conservative mortgage rate
Keep both numbers in view
The construction-phase interest payment helps you budget the build. The permanent mortgage payment tells you whether the finished home still fits. Both matter, but they answer different questions.