Investment Return Formulas
Total return on a lump sum:
FV = PV × (1 + r)^t
PV = initial investment | r = annual return | t = years
CAGR (Compound Annual Growth Rate):
CAGR = (Ending Value ÷ Beginning Value)^(1 ÷ Years) − 1
With annual contributions:
FV = PMT × [(1 + r)^t − 1] ÷ r
PMT = annual contribution (end of year)
North Dakota example — $$11,681/year at 7%:
- After 10 years: $161,390 ($116,810 contributed)
- After 20 years: $478,868 ($233,620 contributed)
- After 30 years: $1,103,396 ($350,430 contributed + $752,966 gains)
Tax note for North Dakota investors: In a taxable brokerage account, investment gains are subject to 2.5% state income tax plus federal capital gains tax (~15% for long-term). Combined rate ≈17.5%, reducing an effective 7% return to approximately 5.8% after tax. Tax-advantaged accounts avoid this drag entirely — use them first.