Maintenance is more of a guess-timate that usually tracks closely with rent, so many investors apply a simple multiplier to account for it, for example 8% of annual rents.

You multiply the total monthly rent increase times 12 times the Gross Multiplier.

If you knew and did nothing you pay medical and other multiplied by 3.

Same cam be achieved while working in an unrelated field, but the timeline is greater, and the amount of effort is multiplied.

Multiply that times the sq ftg of your house.

On a park, you can calculate the NOI by multiplying the number of spaces occupied by the lot rent, and then multiply by 12 months, subtract the expenses (can range from 35-50%, that % depending on the variables above).

You can do some simple math to gauge potential costs, if you know what master electricians charge per hour in your area and add to that the hourly rate for 1 journeyman and 1 apprentice and multiply that by 80 hours you will have a rough idea as to labor costs.

Whatever your total project cost is, if the lender is requiring 10% down you just multiply the two numbers and you get your down payment or "injection".

If you multiply your answer by 4, you get mine. :)

Then I multiply the average $/sf by the sf of the house I'm considering to get the ARV.