I'm toying around with my long term ETF dollar cost average buying system. It goes like this: Use the Shiller CAPE ratio as a guide to how much to invest: When the CAPE ratio is 1.5 standard deviation (sd) above long term mean CAPE ratio (SP500), then invest 70% of usual monthly allotments, saving the remainder in cash or offset When the CAPE ratio drops back below 1.5 sd, invest 130% of usual monthly allotments until 'excess' from scenario 1 depletes At all other times, invest the usual allotment amount Standard deviation cutoff and reduce spend amounts are both arbitrary numbers (I wanted the 'caution' trigger happening enough to be useful, but not too often to be impractical). Using the above system, with CAPE ratios going back to 1881, the reduced spending trigger occurs in 7% of all months. Charted, it looks like the below since 1900 (the labels don't show it, but data goes to April 2020): Note: orange = reduce spend triggered I'm looking to systemise my 'market timing' approach, to avoid letting my emotion or judgement get in the way. Now my question is, does anyone know how I can simulate the returns of using this strategy vs. the benchmark (i.e. just dollar cost average the same amount every month, with no CAPE adjustments)? I want to know if it is actually worth the effort in overall returns (I'm guessing not but it's been a fun exercise to do anyway).