The Compound Interest Workbook
The same verified math as the Compound Interest Calculator — as a sheet you can keep. Enter your starting balance, monthly contribution, return, and years; see future value, contributions vs growth, a year-by-year table, and what a fee drag would cost. Every formula is shown so you can check it.
What's inside
- Inputs: starting balance, monthly contribution, annual return %, years, optional expense-ratio drag
- Outputs: future value, total contributions, total growth, fee-drag column, year-by-year table (matches the calculator's
FV = P(1+i)n + PMT((1+i)n−1)/i) - Disclaimer on every export: "Hypothetical, constant return — real markets vary. See Methodology →"
| Year | Balance (0% fee) | Contributions | Growth | Fee drag at 1% (cost) |
|---|---|---|---|---|
| 1 | $2,312 | $2,200 | $112 | $16 |
| 5 | $8,577 | $7,000 | $1,577 | $251 |
| 10 | $19,318 | $13,000 | $6,318 | $1,111 |
| 20 | $56,131 | $25,000 | $31,131 | $6,617 |
| 30 | $130,114 | $37,000 | $93,114 | $23,640 |
Preview — $1,000 start + $100/mo at 7% (monthly compounding, end-of-month contributions; hypothetical, constant return). Your copy recalculates live. Fee drag = same plan at 1% expense drag. Formula: FV = P(1+i)^n + PMT((1+i)^n−1)/i, i = (7%−fee)/12.
Download XLSX — open live → Try it live in the calculator →
No email needed — free to keep. If this saved you time and you'd like to support us, the weekly primer below is how we grow. One email a week, plain-English, every number sourced. XLSX has live formulas — yellow inputs recalculate instantly (same FV = P(1+i)^n + PMT((1+i)^n−1)/i as the calculator). Google Sheets "Make a copy" will be added alongside; fee-drag view is at /fee-drag.
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How to use it
- Click Make your copy — the Sheet opens in your Google Drive as your own editable copy.
- Change the yellow input cells (balance, monthly, return, years, fee). The table and headline update instantly.
- Use the fee column to see what the same plan costs at 1% vs 0.03% — then try the dedicated Fee Drag Calculator for a side-by-side.
Formulas are in plain Sheets syntax — =FV(rate/12, years*12, -monthly, -start) style — so you can audit every cell. No scripts, no add-ons.
Where this fits
This workbook is the portable version of the site's calculators. Start here, then go deeper:
- Compound Interest Calculator — the interactive version with chart and trail
- Fee Drag Calculator — what a 1% fee costs over 30 years
- How to Invest Your First $1,000 — the article this math comes from
Education, not advice: This workbook is for education only and is not personalized financial advice. It assumes a constant rate of return, which does not happen in real markets. Investing involves risk, including loss of principal. Past performance does not guarantee future results. Every figure is verified against primary sources — see our methodology.