Investment Calculator
Project your investment growth and solve for any variable — contribution amount, required return rate, starting capital, or time horizon — with year-by-year accumulation schedules.
Key Features
- •5 solver modes: End Amount, Additional Contribution, Return Rate, Starting Amount, and Investment Length
- •Solve for any unknown — enter your goal, get the missing variable
- •9 compounding frequencies: Annually, Semiannually, Quarterly, Monthly, Semimonthly, Biweekly, Weekly, Daily, and Continuously
- •Continuous compounding modeled as e^(r/12) growth per month with monthly PMT deposits
- •Lump sum initial investment plus recurring monthly contributions
- •Year-by-year accumulation schedule with deposit, interest, and ending balance
- •Principal vs. interest donut chart for visual breakdown
- •Algebraic solvers for contribution and starting amount; bisection search for return rate, investment length, and all continuous compounding modes
About Investment Calculator
Whether you are just starting to invest or optimizing an existing portfolio, knowing how to project future value — and work backwards from a goal — is essential. Our Investment Calculator gives you five ways to slice the same problem, each solving for a different unknown while holding the rest fixed.
Five Solver Modes
Most calculators only go one direction: enter your inputs, get a future balance. Ours goes all five:
- End Amount: Given your starting capital, monthly contributions, return rate, and time horizon, what will your portfolio be worth?
- Additional Contribution: You have a target. You know your starting amount, expected return, and time. How much do you need to contribute each month?
- Return Rate: You have a target, a starting amount, monthly contributions, and a timeline. What annual return rate do you need to hit it?
- Starting Amount: You have a target, a monthly contribution, a return rate, and a time horizon. How much do you need to invest upfront?
- Investment Length: You have a target, a starting amount, monthly contributions, and a return rate. How many years until you get there?
9 Compounding Frequencies
From annually to continuously, the calculator supports every major compounding interval: Annually, Semiannually, Quarterly, Monthly, Semimonthly, Biweekly, Weekly, Daily, and Continuously. Contributions are always modeled as monthly deposits, scaled correctly to each compounding period so results are mathematically consistent across all frequencies. Continuous compounding applies e^(r/12) growth per month with PMT added each month — the theoretical maximum for a given rate.
Understanding the Accumulation Schedule
The year-by-year schedule breaks down each year's deposit (principal added), interest earned, and ending balance. This makes it easy to see exactly when compounding begins to outpace contributions — the inflection point that defines long-term wealth building.
Goal Seeking in Practice
The four goal-seeking modes use exact algebraic solutions where possible (Additional Contribution, Starting Amount) and high-precision bisection search where closed-form solutions don't exist (Return Rate, Investment Length, and all modes under continuous compounding). Results converge to many decimal places of accuracy.
FAQ: Investment Calculator
What is a good annual return rate?
Historically, the S&P 500 has returned roughly 8–10% annually before inflation. Bonds typically return 4–6%. Money market and high-yield savings accounts currently offer 4–5%. Use these as benchmarks when choosing your return rate input.
What compounding frequency should I use?
Use "Monthly" for most brokerage and retirement accounts. Use "Annually" if your bank or broker quotes an APY directly. "Continuously" is the theoretical maximum and is used in some academic and options pricing contexts.
How is the monthly contribution applied across frequencies?
The monthly PMT is scaled to each compounding period: contributionPerPeriod = PMT × 12 / n. For continuous compounding, PMT is added each month alongside continuous growth. Annual contribution totals remain consistent regardless of frequency.
Investment Calculator is optimized for fast browser-based use, so you can test multiple scenarios in seconds.
Formula & Logic
- 01Discrete FV: balance = P*(1 + r/n)^(n*t) + (PMT*12/n) * ((1 + r/n)^(n*t) - 1) / (r/n), applied n periods per year.
- 02Continuous FV: balance = balance * e^(r/12) + PMT, applied 12 times per year (month-by-month simulation).
- 03Solved PMT (discrete): pmtPerPeriod = (T - P*growthFactor) / ((growthFactor - 1) / (r/n)); monthly PMT = pmtPerPeriod * n / 12.
- 04Solved Starting Amount (discrete): P = (T - annuityFV) / growthFactor, where annuityFV = (PMT*12/n) * ((growthFactor-1)/(r/n)).
- 05Solved Return Rate: bisection over [0%, 100%] with 200 iterations.
- 06Solved Investment Length: bisection over [0, 200] years with 200 iterations.
- 07Continuous modes (Additional Contribution, Starting Amount) also use bisection since no closed-form solution exists.
- 08Schedule: same per-period logic as fv() — yearInterest = endBalance - startBalance - PMT*12.
Practical Examples
- 01Baseline check: Use realistic inputs in Investment Calculator to generate a first-pass estimate.
- 02Sensitivity check: Change one key input at a time to compare how the output shifts.
- 03Decision check: Save two or more scenarios and use the differences to choose the better option.
Important Limitations
- •Results depend on the accuracy of your inputs.
- •Displayed values may be rounded for readability.
- •Financial outputs are planning estimates and do not include institution-specific fees unless provided.
Frequently Asked Questions
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