Investment Calculator

Investment Calculator With Compound Growth Explained

This investment calculator shows how a balance grows over time using compound interest. You can enter an initial deposit, monthly contributions and an expected return rate to estimate your future value.

How compound interest works

Compound interest means you earn interest not just on your contributions but also on interest previously earned. Over time, the growth curve accelerates.

Future Value = P × (1 + r)n + PMT × ( [(1 + r)n – 1] ÷ r )

• P = current balance
• PMT = monthly contribution
• r = monthly return rate (annual rate ÷ 12)
• n = number of months

Example investment scenario

• Initial balance: $5,000
• Monthly contribution: $200
• Expected return: 7% annually
• Investment period: 20 years

Typical results:

• Total contributed: $53,000
• Investment growth: $75,000+
• Future value: $128,000+

This shows how compounding over time generates more growth than contributions alone.

Monthly vs yearly compounding

• Monthly compounding reflects real investing (401k, brokerage, IRA).
• Yearly compounding is more simplified.

This calculator uses monthly compounding for accuracy.

Choosing an expected annual return

Typical long-term historical averages:

• Moderate diversified portfolio: 6%–8%
• High-risk growth: 9%+
• Very conservative: 3%–5%

No rate is guaranteed — calculations are estimates.

Lump-sum vs monthly contributions

Lump-sums perform strongest at the beginning because more time is available for growth.

Monthly contributions benefit from:

• Dollar-cost averaging
• Reduced timing risk
• Better budgeting

The calculator allows comparing both methods.

Frequently Asked Questions

Does this calculator include taxes?
No, it shows growth before taxes. Tax impact depends on investment account type.

Can I model employer matching?
Yes, simply add matching number to monthly contribution.

Can I simulate inflation?
Use our inflation calculator to estimate real purchasing power.

Can investment returns vary?
Yes — long-term estimates smooth volatility into average growth values.

This investment calculator is ideal for retirement planning, long-term savings, 401k projections and comparing growth with different contribution levels.