SIP CalculatorMonthly Investment Growth Calculator
See exactly how much your monthly investments will grow — whether you're building a retirement nest egg, investing in ETFs, or growing a brokerage portfolio.
What is SIP? (Monthly Investing Explained)
SIP (Systematic Investment Plan) is an investing strategy where you contribute a fixed dollar amount every month into market investments such as ETFs, index funds, or mutual funds. Instead of trying to time the market with one large lump sum, SIP lets you invest automatically from each paycheck — building wealth steadily through consistency rather than speculation.
In the US, SIP is the investing philosophy behind every 401(k) payroll contribution, every automatic Roth IRA deposit, and every recurring brokerage purchase. The idea is identical to what financial advisors call dollar-cost averaging — you buy more shares when prices are low and fewer when prices are high, naturally lowering your average cost per share over time.
Whether you're contributing to a 401(k) at work, funding a Roth IRA, or setting up automatic investments in an S&P 500 index fund at a SEC-regulated brokerage like Fidelity, Vanguard, or Schwab — you are already practicing SIP. This calculator lets you project exactly how much that monthly discipline could be worth over 10, 20, or 30 years.
How Monthly Investment Returns Are Calculated
Each monthly contribution begins compounding the moment it is invested. The future value of recurring monthly investments is calculated using the compound annuity formula — the same math that powers every retirement projection tool:
P = Monthly contribution amount
r = Monthly return rate = Annual rate ÷ 12 ÷ 100
n = Total number of months invested
FV = Future portfolio value
Real-world example
Monthly investment: $500 | Expected return: 10% p.a. | Duration: 10 years (120 months)
r = 10 ÷ 12 ÷ 100 = 0.00833
FV = 500 × ((1.00833)¹²⁰ − 1) ÷ 0.00833 × 1.00833
FV ≈ $103,276 | Total Invested: $60,000 | Returns: $43,276
Want to see how a one-time investment grows instead? Try our Compound Interest Calculator.
Why Monthly Investing Works
📅
Removes Emotion from Investing
Automating a fixed monthly contribution means you invest every month — in bull markets and bear markets alike — without second-guessing yourself.
📈
Power of Compounding
Returns earn returns of their own. The longer you stay invested, the faster your portfolio grows — and the gap between what you invested and what you have widens dramatically.
⚖️
Dollar-Cost Averaging
You naturally buy more shares when prices fall and fewer when prices rise. Over decades this lowers your average cost per share without any active management.
🏦
Works with Retirement Accounts
Every 401(k) payroll deduction and IRA auto-contribution is monthly investing in action. This calculator models exactly that discipline — use it to plan any account type.
🔄
Easy to Scale Up
Raise your contribution by 5–7% each year as your salary grows. Even modest annual increases compound into dramatically larger retirement wealth over 20–30 years.
🛡️
Built-in Diversification
Investing monthly into broad index funds or ETFs spreads risk across hundreds of companies — far safer than picking individual stocks.
Monthly Investing vs. Lump Sum
Both strategies can build wealth — but they suit different situations. Most working Americans are already monthly investors: every 401(k) payroll deduction, every scheduled IRA contribution, every automatic brokerage purchase is monthly investing in practice.
| Factor | Monthly (SIP) | Lump Sum |
|---|---|---|
| How it works | Fixed amount every month | One large amount, one time |
| Market timing risk | Low — averages out over time | High — entry point matters a lot |
| Capital needed | $100–$1,000/month to start | $5,000–$50,000+ upfront |
| Best suited for | Salaried workers, IRA/401(k) savers | Bonus, inheritance, tax refund |
| Emotional challenge | Low — automatic and hands-off | High — hard to pull the trigger |
| Long-term outcome | Steady, predictable growth | Volatile — great or poor depending on timing |
The Power of Starting Early
The single biggest variable in long-term wealth building is not how much you invest — it's how early you start. Each monthly contribution starts compounding immediately, and those returns compound on themselves. The result is exponential growth that accelerates the longer you stay invested.
Consider this: someone who starts investing $300/month at age 25 into an S&P 500 index fund will likely retire with significantly more wealth than someone who starts $600/month at age 35 — even though the later investor contributes twice as much per month. Those 10 extra years of compounding are simply irreplaceable. Use our Retirement Calculator to model your specific retirement timeline.
Start at 25, retire at 55
~$1.14M
Total invested: $180K
$500/mo · 30 yrs · 10%
Start at 35, retire at 55
~$383K
Total invested: $120K
$500/mo · 20 yrs · 10%
Start at 45, retire at 55
~$103K
Total invested: $60K
$500/mo · 10 yrs · 10%
Based on 10% annual return — approximating the S&P 500 long-term historical average (1957–2024). Actual returns will vary. Past performance does not guarantee future results.
Disclaimer: Projections are based on assumed rates of return and are for illustrative purposes only. All investments carry risk, including the possible loss of principal. The S&P 500 return of ~10% is a long-term historical average and is not guaranteed. Past performance does not guarantee future results. Consult a licensed financial advisor or fiduciary before making investment decisions.
Frequently Asked Questions
Planning for retirement? Our Retirement Calculator factors in your savings rate, current age, and retirement goal to give you a full picture. To compare how a one-time investment compounds over time, try the Compound Interest Calculator.