We would call that an " Open " mortgage - it helped me pay off my first house 1981-87 by putting $ 50 - 150 against the principle on payday, whenever I could. Standard mortgages would allow a paydown once-per-year on the anniversary - and it was often limited to a given % of principle. < 10 - 20 % iirc ? >
"Open Mortgages" were available but not common then - the rates were higher. The stiff penalties were introduced during that crazy era of interest rates in the early 1980's < I was at 18.5 % for a while in 1982 >
The olde standard, to get out of a mortgage was a 3-month interest penalty - in the early 80's new mortgages quickly became ALL the remaining interest ! That same terrible era also saw the advent of short term mortgages ; eg. 3 month ; variable rate mortgages ; weekly payments ; etc John T.