How This Calculation Works
This calculator projects your retirement balance using the same compound growth math as any long-term investment: your current savings grow on their own through compounding, and your monthly contributions add up over time while also earning returns. The number of years between your current age and retirement age determines how many compounding cycles your money gets to benefit from.
Because retirement timelines are often measured in decades, small differences in contribution amount or rate of return can compound into very large differences in the final balance — this is the single biggest reason financial advisors emphasize starting early, even with modest amounts.
This projection doesn't account for employer matching contributions (if applicable, add your match to your monthly contribution), taxes on withdrawal, or required minimum distributions — it's a simplified model for directional planning, not a substitute for a full retirement plan.
Common Mistakes to Avoid
- Leaving employer match on the table. If your employer matches 401(k) contributions up to a certain percentage, not contributing enough to get the full match means turning down free money — add the match amount to your monthly contribution here.
- Using too aggressive a return assumption. Assuming 10%+ returns for decades can produce an overly optimistic projection. A more conservative 6–7% assumption for a diversified portfolio gives a safer planning buffer.
- Not increasing contributions over time. This calculator assumes a flat monthly contribution, but in reality most people can increase contributions as income grows. Revisit the numbers periodically with updated, higher contribution amounts.
- Forgetting inflation erodes purchasing power. A projected balance of $1 million in 30 years won't have the same purchasing power as $1 million today. Consider using an inflation-adjusted return rate (subtract ~2–3% from your assumed return) for a more realistic picture.
Worked Example
Scenario: Currently 30 years old, planning to retire at 65 (35 years), with $15,000 saved, contributing $400/month, expecting a 7% annual return.
Step 1 — Monthly rate: 7% ÷ 12 ≈ 0.583% per month, over 35 × 12 = 420 months.
Step 2 — Growth of current savings: $15,000 × (1.00583)⁴²⁰ ≈ $166,240.
Step 3 — Growth of contributions: $400 × [((1.00583)⁴²⁰ − 1) ÷ 0.00583] ≈ $637,470.
Step 4 — Projected total: $166,240 + $637,470 ≈ $803,710 at retirement.