Monthly Investment Calculator
The Monthly Investment Calculator projects how regular monthly investments grow over time — the strategy known as dollar-cost averaging (DCA). Whether you're contributing to a 401(k), a Stocks and Shares ISA, or a regular brokerage account, this calculator shows how consistent monthly investing builds wealth through the power of compounding.
Educational estimate. Calculator results are for planning and information only, not financial, tax, medical, legal, or engineering advice. Verify important decisions with official sources or a qualified professional.
Monthly Investment Calculator
Dollar-Cost Averaging & Recurring Investment Projector
📐 Formula & Method
Future Value of Regular Contributions
Where PMT = monthly contribution, r = monthly return rate (annual ÷ 12 ÷ 100), n = total months (years × 12). This is the future value of an annuity-due formula.
📋 How to Use
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Enter your fixed monthly investment amount.
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Enter your expected annual return rate (8% is a common long-term equity estimate).
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Enter your investment period in years.
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Click Calculate to see projected final value, total invested, and total gain.
Dollar-Cost Averaging: The Strategy Behind Regular Investing
Dollar-cost averaging (DCA) is an investment strategy where you invest a fixed amount at regular intervals — monthly, biweekly, or weekly — regardless of market conditions. When markets are down, your fixed contribution buys more shares at lower prices. When markets are up, it buys fewer but appreciates more. Over time, this averages out the cost per share and reduces the impact of short-term market volatility.
DCA is the strategy embedded in 401(k) and workplace pension contributions — most workers contribute a fixed percentage of each paycheck automatically. In the UK, auto-enrolment pension contributions work the same way: a set percentage invested every payday. This "set it and forget it" approach has made regular investing accessible to millions who would otherwise struggle to time the market.
$500/month invested at 8% annually for 20 years grows to approximately $294,000 — from $120,000 in total contributions. For 30 years at the same rate: $745,000 from $180,000 contributed. The investment gain ($565,000) is more than three times the amount contributed — purely from compound returns on regular contributions.
For US investors, the 2024 contribution limits are: $23,000 for a 401(k) ($30,500 if 50+), $7,000 for a Traditional or Roth IRA ($8,000 if 50+). For UK investors, the annual ISA allowance is £20,000, and auto-enrolment pension minimum contributions are 5% employee + 3% employer. Maximising tax-advantaged accounts before taxable investing is universally recommended.
🔬 Methodology & Accuracy
Formula: Uses the standard mathematical formula shown in the Formula & Method section above. All computations run client-side in your browser — no data is sent to our servers.
Data sources: Tax bands, contribution limits and regulatory rates are taken from official US (IRS, SSA) and UK (HMRC, gov.uk) publications for the current tax year, and updated when bands change.
Last reviewed: June 2026 · Accuracy: Results are precise to two decimal places using IEEE-754 double-precision arithmetic. Intended for educational and planning use only.
For informational purposes only. Results are estimates based on the inputs and formulas provided. For financial, tax, medical, or legal decisions, consult a qualified professional. Rates and regulations change — always verify current figures with official sources.