Compound growth results
$1,250,000
*Year‑end balance, showing compound growth with chosen frequency.
Compound interest: the eighth wonder of the world
Compound interest means you earn interest not only on your original savings but also on the interest you've already earned. Over long periods, this creates exponential growth. For retirement, starting early is crucial: a 40‑year‑old with $50k, adding $500/month at 7% compounded monthly, will have over $1.27M at 65. Total contributions are just $200k – the rest is compound earnings.
How compounding frequency matters
Compounding monthly (n=12) yields slightly more than quarterly (n=4) or annually (n=1) because interest is added to principal more frequently. Our calculator uses the formula FV = PV × (1 + r/n)^(n·t) for the lump sum, and for monthly contributions we apply the annuity formula adjusted for frequency.
Example: $50k today, $500/month, 7% annual, compounded monthly for 25 years. Future value = $50k × (1+0.07/12)^(300) + $500 × [((1+0.07/12)^(300)-1)/(0.07/12)] ≈ $1,274,000. Total contributions = $50k + $500×300 = $200k. Interest = $1,074,000.
Why start early? The last 10 years of contributions have less time to compound. This tool's yearly table shows the accelerating effect.
Use these calculations as an informational basis only. Do not make financial, legal, or retirement decisions based solely on these results.
Frequently asked questions
What is compound interest in retirement planning? Earning returns on both your principal and previous returns – it's what makes savings grow faster over time.
How often should interest be compounded? More frequent compounding (monthly vs annually) yields slightly higher returns. Most retirement accounts compound daily or monthly.
Does compounding frequency matter? Yes, but the difference between monthly and daily is small. Monthly is a good standard.
What rate of return should I assume? For a balanced portfolio, many use 6‑8% historical average. Be conservative.
How accurate is this retirement calculator? It uses standard compound interest formulas; actual returns vary, but it's an excellent planning tool.