Final Balance
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Interest Earned
—
Total Return
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Principal$10,000
Annual rate7%
Years20 years
Compounding
Balance over time
Formula: A = P(1 + r/n)^(nt) — P: principal · r: annual rate · n: periods/year · t: years
Monthly Required
—
Total Contributed
—
Interest Earned
—
Target amount$50,000
Current savings$5,000
Annual rate6%
Years to goal10 years
Progress to goal
Formula: PMT = (FV − PV×(1+r)^n) × r / ((1+r)^n − 1)
Years to Double
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Years to 4×
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Rate for 10yr Double
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Annual rate8%
Starting amount$10,000
Doubling periods
Formula: Years to double ≈ 72 / rate — quick mental math for compound growth. More precise: 69.3 / rate.
Final Value
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Total Invested
—
Total Gain
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Monthly investment$500
Annual return8%
Years20 years
Invested vs total value over time
Formula: FV = PMT × ((1+r)^n − 1) / r — regular monthly contributions compounding over time
Monthly Payment
—
Total Interest
—
Total Cost
—
Loan amount$300,000
Annual rate6.5%
Term30 years
Principal vs interest paid over time
Formula: M = P × r(1+r)^n / ((1+r)^n − 1) — standard amortization
Months to Payoff
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Total Interest
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Total Paid
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Balance$5,000
APR22%
Monthly payment$200
Balance paydown over time
Tip: minimum payments can take 10+ years — every extra dollar on payment cuts months and saves more in interest
Nest Egg
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Monthly Income
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Years to Retirement
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Current age30
Retirement age65
Current savings$25,000
Monthly contribution$500/mo
Expected return7%
Withdrawal rate4%
Portfolio growth to retirement
Based on the 4% rule — annual safe withdrawal rate historically sustainable over a 30-year retirement
Future Cost
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Purchasing Power Lost
—
Real Value in Today's $
—
Current amount$10,000
Inflation rate3%
Years20 years
Purchasing power erosion
Formula: Future Cost = P × (1+r)^t — how much you'll need in the future to buy what $P buys today
Final Value
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Total Contributed
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Total Gains
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Initial investment$10,000
Monthly addition$200/mo
Annual return8%
Years25 years
Growth with regular contributions
Combines lump-sum compound growth with future value of an annuity for monthly contributions
Net Present Value
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Decision
—
Sum of Cash Flows
—
Discount rate10%
Cash flows — Year 0 is typically the initial investment (negative)
Cash flows by year
Formula: NPV = Σ CF_t / (1+r)^t — positive NPV means the investment creates value at your discount rate
Break-even Units
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Break-even Revenue
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Contribution Margin
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Fixed costs / month$10,000
Price per unit$50
Variable cost / unit$20
Revenue vs total costs
Formula: Break-even units = Fixed Costs / (Price − Variable Cost per unit)
ROI
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Annualized ROI
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Net Gain
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Initial investment$10,000
Final value$15,000
Duration3 years
Investment growth curve
ROI: (Final − Initial) / Initial × 100 · Annualized: (Final/Initial)^(1/t) − 1