How it works
Each month, the calculator grows the balance by the expected return minus the TER, divided by 12 to get a monthly rate, and then adds your contribution. To show what the fees cost, it runs the same plan a second time without the TER: the gap between the two final values is the cost of the TER, including the growth the fees would otherwise have earned. Purchasing power (real) divides the nominal final value by the cumulative inflation over the whole period, so it shows the result in today's money. Total paid in is the initial investment plus all monthly contributions. Worked example with the default inputs (1,000 initial investment, 300 per month, 7% return, 0.2% TER, 2% inflation, 25 years): the plan ends at about 240,917 nominal, or about 146,846 in today's money, with 91,000 paid in; the TER costs about 7,830 along the way.
Read the results as one possible path under fixed assumptions, not as a forecast. Real returns vary from year to year, and for a savings plan the order of good and bad years matters. The model keeps the return, the TER and inflation constant for the entire period and ignores taxes, transaction fees, spreads and tracking differences. Try several return assumptions, including low ones, to see how sensitive the result is.