[punky]

Here's my mortgage length calculator:

Spoiler: 

I'm sure there's a way to do it without a loop, but can't think of it atm.

Assuming £100,000 with a 4.75% rate and paying off £700/month

            float mortgage = 100000f;
            float rate = 4.75f; //%
            int repaymentAmount = 700;

            float months = 0;

            while (mortgage > 0)
            {
                mortgage *= (1 + ((rate / 12) / 100));
                mortgage -= repaymentAmount;
                months++;
            }

            Console.WriteLine("Repayment duration: " + months + " months - " + (int)(months/12) + " Years and " + (months%12) + " months.");

Result:

Repayment duration: 211 months - 17 Years and 7 months.