Investment Growth Calculator
Calculate how your investments grow over time with compound interest, regular monthly contributions, and optional inflation adjustment. See a year-by-year breakdown, total interest earned, real purchasing power, and Rule of 72 doubling time.
Investment Details
Regular amount added each month (optional)
Shows inflation-adjusted real value alongside nominal balance
Final Balance after 20 years
$160,409.35
Balance Breakdown
Rule of 72
Doubles every 9 years
at 8% annual return
Year-by-Year Growth
| Year | Balance | Contributed | Interest (yr) | Total Interest |
|---|---|---|---|---|
| 1 | $13,286.78 | $12,400.00 | $886.78 | $886.78 |
| 2 | $16,836.50 | $14,800.00 | $1,149.72 | $2,036.50 |
| 3 | $20,670.20 | $17,200.00 | $1,433.70 | $3,470.20 |
| 5 | $29,282.21 | $22,000.00 | $2,071.62 | $7,282.21 |
| 10 | $57,614.09 | $34,000.00 | $4,170.28 | $23,614.09 |
| 15 | $99,242.93 | $46,000.00 | $7,253.90 | $53,242.93 |
| 20← final | $160,409.35 | $58,000.00 | $11,784.75 | $102,409.35 |
How It's Calculated
Initial Investment: 10,000.00
Annual Return Rate: 8%
Compound Frequency: monthly
Investment Period: 20 years
Monthly Contribution: 200.00
Total Contributed: 58,000.00
Effective Monthly Rate = (1 + 8%)^(1/12) − 1 = 0.6434%
Final Balance: 160,409.35
Total Interest Earned: 102,409.35
Rule of 72: 72 ÷ 8% = 9 years to doubleWhat Is an Investment Growth Calculator?
An investment growth calculator projects how a lump-sum investment—or a combination of initial capital and regular monthly contributions—grows over time through the power of compound interest. By entering your starting amount, expected annual return, investment period, and optional monthly deposits, you get an instant projection of your final balance, total interest earned, and a year-by-year growth table.
Whether you're planning for retirement, building an emergency fund, saving for a home deposit, or just exploring "what if" scenarios with different return rates and timelines, this tool makes it easy to visualise the long-term impact of consistent investing.
How to Use This Calculator
Enter your starting amount
Type your initial lump-sum investment. If you're starting from zero with only monthly contributions, enter 0 or leave it blank — monthly contributions alone will still build significant wealth over time.
Set your monthly contribution
Add the amount you plan to invest each month. This is where the 'investment snowball' effect is most dramatic. A $200/month contribution at 8% over 30 years produces more than $290,000 in total — from just $72,000 in actual deposits.
Choose your return rate and period
Enter your expected annual return and how many years you'll invest. Use the quick presets (e.g. 10yr / 8%) for common scenarios. Drag the sliders to explore different assumptions interactively.
Review the year-by-year table
The growth table shows your balance, contributions, and interest for each year. Click 'Show all years' for the complete breakdown. Add an inflation rate to see the real purchasing power of your future balance in today's money.
The Investment Growth Formula
Lump Sum Only
FV = P × (1 + r/n)^(n × t)
P = principal r = annual rate n = compounds/year t = yearsThe classic compound interest formula. Your principal grows exponentially as interest earns interest. At 8% compounded monthly for 20 years, $10,000 becomes $49,268 — nearly 5× your original investment.
With Regular Contributions
FV = P(1+r)^t + PMT×[((1+r)^t−1)/r]
PMT = periodic contribution r = rate per period t = periodsRegular contributions (PMT) are added via the annuity formula. Each contribution itself earns compound interest from the day it's made. This is why starting early is so powerful — even small amounts deposited consistently grow into large sums.
Worked Example — The Power of Starting Early
Two investors both contribute $300/month at 8% annual return (compounded monthly). The only difference is when they start:
| Investor | Starts at | Years invested | Total deposited | Balance at 65 |
|---|---|---|---|---|
| Alex (early starter) | Age 25 | 40 years | $144,000 | $1,007,000+ |
| Sam (late starter) | Age 35 | 30 years | $108,000 | $446,000+ |
| Jordan (very late) | Age 45 | 20 years | $72,000 | $177,000+ |
Key Insight:
Alex deposits just $36,000 more than Sam over their investing career, yet ends up with $561,000 more at retirement. That extra decade of compounding is worth over half a million dollars. This is why the most important investing decision you can make is simply to start — even with a small amount.
Reproduce Alex's scenario: Initial $0 · Monthly $300 · Rate 8% · 40 years in the calculator above.
Typical Investment Return Rates
Use these historical averages as a starting point for your return rate assumption. Remember: past performance does not guarantee future results.
| Asset Class | Nominal Return | Real Return (~2.5% inflation) |
|---|---|---|
| US Stocks (S&P 500) | ~10%/yr | ~7%/yr |
| Global Equities (diversified) | 7–9%/yr | 4.5–6.5%/yr |
| Government Bonds | 3–5%/yr | 0.5–2.5%/yr |
| Corporate Bonds | 4–6%/yr | 1.5–3.5%/yr |
| REITs (Real Estate) | 8–12%/yr | 5.5–9.5%/yr |
| High-Yield Savings Account | 3–5%/yr | 0.5–2.5%/yr |
| Cash / Money Market | 1–4%/yr | −1.5–1.5%/yr |
Historical averages (US market, long-term). Actual returns vary significantly by period and geography. Always consult a financial advisor before making investment decisions.
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