Repayment Mortgage vs Investment Based Mortgage Calculator This calculator estimates the total cost of buying a house comparing the repayment mortgage with the investment (i.e. ISA) based one. Experiment with different inflation and investment growth assumptions. This will highlight that the choice of mortgage is very much dependent on your view of the future. A balanced view for the traditional 20-25 year mortgage might be to go for the investment route, but with the monthly investment being made in the expectation of low investment returns. That way any extra performance feeds into a useful surplus. For shorter terms (under 10 years), investment volatility swings the view towards the certainty of the repayment route. Intermediate terms are very much dependent upon one's personal position and attitude towards risk and reward. Your property may be repossessed if you do not keep up repayments on your mortgage. Mortgage required: * Expected Investment Growth: * Term of Mortgage: * Enter in years. Interest rate: * Enter 7% as 7.