Investment Growth Planner (US)

Compounding is simple. Knowing which account to put the money in is not.

The free Compound Interest Calculator shows raw growth. But your real outcome depends on which accounts you use — Roth IRA (tax-free withdrawals), Traditional IRA/401(k) (tax-deferred), or taxable brokerage (capital gains). This planner models all of them together so you can see your actual after-tax wealth at retirement, not just a headline number.

What's Included

• Multi-account modelling: enter current balance and monthly contribution for each account type — Roth IRA, Traditional IRA, 401(k)/403(b), HSA, and taxable brokerage
• Contribution limit tracker: shows current annual limits for each account type, flags when you're maxing out, and suggests overflow order (401k match → Roth IRA → 401k max → taxable)
• After-tax projection: models the tax impact at withdrawal — Roth is tax-free, Traditional is taxed as income, taxable accounts pay capital gains. Shows your real spendable income at retirement, not just the portfolio value
• Fee impact comparison: enter your expense ratio (e.g. 0.03% for VTI vs 1.0% for an advisor-managed fund) — see the dollar difference over 10, 20, and 30 years. The gap is usually tens of thousands.
• Employer match calculator: enter your company's match formula — the sheet shows total annual contribution including match and the "free money" you leave on the table at lower contribution levels
• Drawdown phase modeller: at what age do you start withdrawing? Enter target retirement age and monthly spending need — the sheet shows how long your portfolio lasts under different withdrawal rates (3%, 3.5%, 4%, 4.5%)
• Scenario comparison: see three scenarios side by side — conservative (5%), moderate (7%), aggressive (9%) — so you can plan for the realistic range, not just the optimistic case
• 10/20/30 year milestone chart: visual progress bars showing projected portfolio value at each decade
• Works in Google Sheets (free) and Excel

Who This Is For

• Young investors (20s–30s) who have started contributing but aren't sure they're using the right account types in the right order
• Anyone maxing out their 401(k) match who wants to know what to do with the next dollar
• People paying high fund fees who want to see the actual long-term cost before switching
• Anyone planning early retirement who needs to model the Roth conversion ladder or taxable bridge strategy

How It Works

1. Enter your age, target retirement age, and each account's current balance
2. Set monthly contributions per account — the sheet flags if you're over annual limits
3. Enter your expected return rate and fund expense ratio
4. The projection shows after-tax portfolio value at retirement, monthly income you can withdraw, and how long it lasts
5. Adjust scenarios to see how saving more, paying lower fees, or retiring earlier changes the outcome