Cap Ex....an investment killer?

[Jordan Fujan]

I'm working on my investment spreadsheet and have been doing some reading on the topic of Cap Ex. Some people use a number like 10% of the income, but many suggest itemizing your expenses over their lifespan is the most accurate. I've seen some logical points made that under estimating Cap Ex may not be realized until many years later when a few larger than expected expenses eat up years of "cash flow".

Below is my Cap Ex estimate. I've taken the lifespan and current age of the item (many do not add current age but I don't understand how you can be accurate without it) into account to estimate the remaining years until replacement is needed. For a SFH that rents for $1800 that would be 17% Cap Ex. I understand that Cap Ex is location and age of home dependent, but is it possible for this to be ballpark accurate for these times? I wonder if 10% is so commonly used because people are looking at 10 yr time frames and not 30+? Am figuring these numbers right? Any other variables I'm not looking at?

Your input is appreciated!