What annual return should I use?

The US stock market (S&P 500) has averaged approximately 10% annually before inflation over the long term. After inflation, the real return is closer to 7%. For conservative planning, many financial advisors recommend using 6–8% for diversified long-term portfolios. For bonds or stable value funds, use 3–5%.

How much should I save per month?

A common guideline is to save 15% of gross income for retirement. For a $60,000/yr salary, that is $750/month. Starting early matters enormously — $500/month invested from age 25 at 8% grows to approximately $1.74 million by age 65, compared to $875,000 starting at age 35.

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Investment Growth Calculator (2026) — Compound Interest & Future Value

Q: What is compound interest?

Compound interest means you earn interest on both your original principal and on previously accumulated interest. Over time, this creates exponential growth. A $10,000 investment at 10% annually becomes $25,937 after 10 years — not $20,000 — because each year's interest earns its own interest.

Written by James Carter | Financial Analyst 🕐 Last Updated: August 2026

Calculate how any investment grows over time using compound interest. Enter your initial investment, monthly contributions, expected annual return, and time horizon to see your projected future value. Based on standard compound interest formulas used by the SEC's investor education resources.

📈 Investment Growth Calculator

Initial Investment ($)

Monthly Contribution ($)

Amount added every month

Annual Return Rate (%)

S&P 500 historical avg ~10% · Conservative: 6–7%

Investment Period (Years)

$0 Future Value

$0Total Contributed

$0Interest Earned

0×Return Multiple

$0Avg Monthly Growth

Initial Investment—

Monthly Contributions Total—

Total Money Invested—

Compound Interest Earned—

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Contributions vs Growth

Contributed Growth

How Compound Interest Works

Compound interest is the mechanism behind long-term wealth building. Unlike simple interest — which only earns returns on your original principal — compound interest earns returns on your principal and on the accumulated interest from previous periods. Over decades, this creates exponential rather than linear growth.

The standard compound interest formula used by this calculator is:

      FV = P × (1 + r)^n + PMT × [((1 + r)^n − 1) / r]

      Where: P = initial amount, r = monthly rate, n = months, PMT = monthly contribution

Power of Starting Early

Time is the most powerful variable in compound interest. Consider this comparison at 10% annual return:

Start Age	Monthly Contribution	Years Invested	Total Contributed	Value at Age 65
Age 25	$500/mo	40 years	$240,000	$3,162,000
Age 35	$500/mo	30 years	$180,000	$1,131,000
Age 45	$500/mo	20 years	$120,000	$382,000
Age 55	$500/mo	10 years	$60,000	$102,000

Starting at 25 vs 35 costs only $60,000 more in contributions but produces nearly 3× more wealth at retirement. The extra decade of compounding makes all the difference.

What Annual Return Rate Should I Use?

10% — US stock market (S&P 500) historical average before inflation
7% — After inflation (real return) for diversified stock portfolio
6–8% — Conservative long-term planning rate used by most financial advisors
4–5% — Balanced portfolio (mix of stocks and bonds)
3–4% — Bond-heavy or stable value portfolio

💡 Disclaimer: Past market returns do not guarantee future performance. This calculator provides educational estimates only. Consult a licensed financial advisor before making investment decisions. See the SEC investor education resources for guidance on realistic return assumptions.

Frequently Asked Questions

What is compound interest?

Compound interest means you earn returns on your original principal plus all previously earned interest. Over long periods, this creates exponential growth. A $10,000 investment at 10% annually becomes $25,937 after 10 years — not $20,000 — because each year's gains earn their own returns the following year.

What annual return rate should I use?

The US stock market has historically averaged ~10% annually before inflation. After inflation, the real return is closer to 7%. Most financial planners use 6–8% for diversified long-term projections. Use 4–5% for balanced portfolios and 3–4% for conservative bond-heavy approaches.

How much should I contribute per month?

A common guideline is to save 15% of gross income. For a $60,000/year salary, that is $750/month. If you are starting late, increase contributions to compensate for lost compounding time. Even small increases — $50–$100/month more — produce significant results over 20–30 year periods.