Expanding on doneby35's answer:
Of the 4 components of the traditional mortgage payment (PITI), the Interest, Taxes, and Insurance clearly count towards the 25% spending.
The Principal portion could arguably count towards your savings rate, but since it's not practically "extractable" as an investment, I would exclude it entirely (count it as neither towards the 25% nor towards the 75%). In the first few years of a 30-year mortgage, the principal payment is small anyway, so it's safe to ignore either way.