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system
need a formula to determine monthly payments received at time t if i'm reinvesting my returns
user
with 10% return over three years, depositing $900 each month, in three years $34,039.30.  re. downvote. i guess this is too brief and without explanation, but i was rushing.  if you want further explanation of how this is calculated check the link already posted by joetaxpayer, and have a look at the formula for continuously compounded return.  also, try out the numbers in the simplified example below yourself.  e.g.  addendum mhoran_psprep has pointed out that i didn't read the op's post closely enough.  with rolling investments the total return will be:  where n is the month number i.e. 36, 37, etc.
assistant