I am 79 years old and have owned houses and investment properties for 52 years. In all that time I have never had a mortgage mature at 30 years. I have always ended up moving or refinancing and paying off a mortgage early. In fact in the US the average length of home ownership is 8 years and the median is 15 years.
Doing these calculations is usually nothing more than a mathematical exercise, and has very little bearing on your day-to-day financial well being. And, when moving, having paid down an extra $10k on your principal has very little bearing on what house you can afford, although it will certainly negatively effect your standard of living.
I find it far better to invest regularly (pay yourself first), get a mortgage which is affordable under that saving regime, and then either invest any money left over or spend it on necessities.
You’re a smarter man than me Ganga Dinn.