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Retirement Calculator
Plan your retirement by calculating how your investments will grow over time with compound interest.
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Retirement Calculator | Long-term Investment Growth
Plan your retirement by calculating how your investments will grow over time with compound interest.
Key values: $50,000 start · $800/month · 7% annual · 25 years
Starting Early at 25 — Minimal Contribution
$5,000 saved at 25, adding just $300/month at 7% for 40 years.
Key values: $5,000 start · $300/month · 7% annual · 40 years
The Power of Compound Interest
A one-time investment of growing at annual rate for years becomes:
where is the compounding frequency (12 for monthly, 365 for daily). With continuous compounding:
Growth with Regular Contributions
Most retirement savings involve monthly contributions . The future value of a series of equal payments (annuity):
Total retirement balance = lump sum growth + contribution growth:
The Rule of 72
A quick mental math shortcut to estimate how long it takes to double your money:
| Return | Doubling time | Example |
|---|---|---|
| 4% | 18 years | Bonds |
| 7% | 10.3 years | Stock market average |
| 10% | 7.2 years | Growth stocks |
| 12% | 6 years | Aggressive growth |
Why Starting Early Matters
Example: Person A invests $500/month starting at age 25. Person B invests $500/month starting at age 35. Both earn 7% annually and retire at 65.
- Person A (40 years): $1,197,811 from $240,000 invested
- Person B (30 years): $566,765 from $180,000 invested
Person A invested only $60,000 more but ended up with over twice the balance. The extra 10 years of compounding — not the extra contributions — account for most of the difference.
Frequently Asked Questions
How much do I need to retire?
A common guideline is to save 25 times your expected annual expenses (the 4% rule). If you plan to spend $50,000 per year in retirement, aim for a portfolio of $1,250,000. The exact amount depends on your lifestyle, healthcare costs, inflation assumptions, and other income sources like Social Security.
What is the Rule of 72?
The Rule of 72 is a mental math shortcut: divide 72 by your annual return percentage to estimate how many years it takes to double your money. At 7% returns, your money doubles in roughly 72/7 = 10.3 years. At 10%, it doubles in about 7.2 years.
Why does starting to save early matter so much?
Compound interest grows exponentially over time. Someone investing $500/month from age 25 to 65 at 7% accumulates roughly $1,200,000, while starting at 35 yields only about $567,000. The extra 10 years of compounding more than doubles the result, even though the additional contributions are only $60,000.
What is the difference between monthly and annual compounding?
Monthly compounding applies interest 12 times per year instead of once, so each month's interest earns interest in subsequent months. The difference is small for short periods but grows over longer horizons.
How do regular contributions affect compound growth?
Regular contributions dramatically accelerate growth because each payment starts compounding from the date it is made. A $100,000 lump sum at 7% for 30 years grows to about $761,000, but adding $500/month on top produces roughly $1,330,000 -- nearly double, with contributions totaling only $180,000.
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