Index funds have averaged ~10% annual returns historically. See how contributions compound over decades.
$500/month invested in an S&P 500 index fund at 10% returns grows to ~
Use this calculator before making any financial commitment that depends on this type of calculation. Running the numbers in advance lets you evaluate options without the pressure of a live negotiation or decision deadline.
The most consequential mistake is comparing financial figures that are not on the same basis — gross versus net, before-tax versus after-tax, or nominal versus inflation-adjusted. Always check whether figures you are comparing use the same definition.
A first-time buyer models three scenarios before making an offer: 10%, 15%, and 20% deposit on a £280,000 property. The calculator shows exactly how the monthly payment and total interest cost change with each deposit level, making the decision visible rather than speculative.
S&P 500 has returned ~10% annually since 1926. Inflation-adjusted: ~7%.
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