Investment Return Calculator

How to use this investment calculator

1. Enter your initial investment amount and the number of years you plan to invest.
2. Set your monthly contribution and expected annual return rate.
3. Choose your compounding frequency (monthly or annually).
4. Toggle "Compare two scenarios" to see how different contribution amounts or rates affect your returns.

Why small differences in assumed return compound into large differences over decades

A 6% versus 8% average annual return sounds like a small gap, but over 30 years, that difference compounds into a dramatically different ending balance, often 50%+ more, not the roughly-30%-more that a linear intuition would suggest. This is exactly why fund fees matter so much over long horizons: a 1% annual fee doesn't just cost 1% once, it costs 1% of a compounding balance every single year, which adds up to a large chunk of total returns over a multi-decade investment.

Frequently asked questions

What return rate should I assume?

There's no reliable way to predict future returns. This tool is for modeling scenarios and comparing assumptions, not forecasting. Try a range (conservative, moderate, optimistic) rather than trusting a single number.

Does it account for taxes on investment gains?

No. This models gross investment growth. Actual after-tax returns depend on account type (taxable, IRA, 401(k)) and your tax situation, which this tool doesn't attempt to estimate.

What does the side-by-side comparison show that running it twice wouldn't?

Mainly convenience and accuracy. Comparing two scenarios manually means re-entering numbers and risking a typo in one run; the side-by-side view holds both fixed so you're comparing exactly what you intended to change.