Commercial Mortgage - Principal Amortization Calculation
I am going to use the figures below for example purposes with my question at the bottom...hopefully it will make more sense.

&amp;#x200B;

**Mortgage A**

* Term: 5 Years (60 Months)
* Floating or Fixed?: Floating
* Interest Only: 2 Years
* Principal: $100,000,000
* Amortization Period: 30 Years (360 months)
* Interest Calc: Actual/360
* Rate: 1 Month LIBOR + 1.95%

&amp;#x200B;

1. At the start of Year 3 (Month 25),  would I utilize the floating rate at Month 25 (and each month moving forward) for the principal amortization or should I assume the loan documents have a amortization constant (e.g. 3.00% fixed for the term)? 
2. For each future monthly principal payment, would I calculate the principal payment by utilizing the previous month's principal balance or the beginning principal balance at loan closing($100M)?
3. For the loan amortization period (30 years or 360 months in this example), would I reduce the amortization period based on how many months have been previously amortized? e.g. Month 27 in our example (2 months previously amortized) would then recalculate the amortization period from 300 months to 298 months.

Apologies I am incorrectly asking the question. I have been struggling with this for years trying to find clarity.
[{"id": "imq9q1e", "text": "The basic answer is that you use the remaining principal as of the month in question as your present value and amortize that to 0 over the remaining months in the original amortization schedule using the new monthly interest rate.\n\nThe effect of this is that the payment amount will fluctuate with the rate, but the amortization schedule will stay the same and zero out on the same payment schedule as originally conceived at funding.\n\nThis kind of loan is relatively uncommon in CRE because it's management intensive (for borrowers and lenders) and borrowers tend to look for debt service stability if they're borrowing against income producing assets. The cheapest sources of debt capital also don't offer amortizing variable rate options.", "replies": [], "depth": 1}]