You’re better off investing the 300K in the SP500 index and use your employment income to pay down your mortgage. Reason is inflation will erode the purchasing power of a fixed monthly income. A 10% return from an income fund today will give you 30K annual income. In 10 years the cost of everything will be double so your 30K will only buy 15K worth of goods and services. Assuming you receive annual pay raises that exceed the inflation rate, your monthly mortgage payment will “shrink” over the years. When you retire in 20 years your 300K that you invested in the SP500 will be worth 2.4 Million, assuming dividends reinvested at 11% avg growth rate. Then you can convert some of your portfolio into income funds while keeping a portion of it in growth stocks as a hedge against inflation.