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Monthly annuity

Save a fixed amount each month, or take a fixed monthly payout from a starting corpus.

Formulas

Save:    FV  = PMT · ((1 + r)n − 1) / r
Withdraw: PMT = PV  · r / (1 − (1 + r)−n)

r = monthly rate (annual / 12 / 100), n = number of months (years × 12).