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Need a formula to determine monthly payments received at time t if I'm reinvesting my returns
How does compounding of annual interest work? answers this question. It's not simple compound interest. It's a time value of money calculation similar to mortgage calculations. Only the cash flow is the other way, a 'deposit' instead of 'payment'. When using a finance calculator such as the TI-BA35 (Note, it's no longer manufactured, but you can find secondhand. It was the first electronic device I ever loved. Seriously) you enter PV (present value) FV (future value) Int (the interest rate) nPer (number of periods) PMT (payment).  For a mortgage, there's a PV, but FV = $0. For you, it's reversed. PMT on this model is a positive number, for you it's negative, the amount you deposit. You also need to account for the fact that a mortgage is paid on day 31, but you start deposits on Day 1. See the other answer (I linked at start) for the equations.