Survey said that average Australian paid off their mortgage within 10 years, despite the average mortgage term is 30 years. This is probably due to the fact that interest rates has been declining for the past many years and Australian have been good with minimizing their spending.
While there are many calculators in the Internet, I find none serve the basic planning of extra prepayments (including the interest rate changes, planned bonuses, tax return, or planned large holiday).
Attached is a template and sample where you can tweak around and plan what your future balance may be like. See how soon you will be able to pay off your mortgage.