Shaun GrahamFinance
Planning tool

Compound Growth Planner

Most compound interest calculators draw one confident line from one contribution you'll supposedly never change. This one models real life — deposits that grow with your raises, a windfall in March, a pause while you switch jobs — against a range of returns, and shows the day your money starts out-earning you.

Private by design: Calculator inputs are processed locally in your browser. They are not transmitted to Shaun Graham Finance or any third party. Nothing is kept unless you ask — use Save to file near the bottom of the page to keep your own copy.

1

Set the assumptions

The three return rates draw a range, not a promise. 4% / 7% / 10% is a common set of conservative-to-optimistic long-run stock market assumptions before inflation.

2

Add contributions

"Raise yearly" is the feature most calculators skip: set it to your expected raise and the deposit grows with your salary instead of staying frozen for 30 years.

TypeAmountRepeatsDate / first depositLast depositRaise yearly
Add a recurring contribution to see compounding work.

Leave "Last deposit" empty to contribute for the whole horizon. Pauses are easy: end one recurring row, add another that starts later.

3

Read the result

Enter your plan to see it grow.
Balance at the horizon$0
In today's dollars$0
You put in$0
Growth does the rest$0
Your money out-earns you—first month lifetime growth exceeds lifetime deposits
Cost of waiting 5 years to start$0same plan, startedlate

Deposits vs. compounding

You put inGrowthReturn range
Balance, contributions, and growth by monthEnter a plan to see contributions and growth stack over time.
Enter a plan to inspect it month by month.
Year-by-year (expected return)
YearYou put inGrowthEnd balanceIn today's dollars

Everything is calculated in your browser; nothing you enter is sent to Shaun Graham Finance. Nothing is stored on this device unless you check the box above; with it clear, a refresh starts from the defaults. When checked, the whole form — including balances and contribution details — is kept in local browser storage, not cookies. That storage is not encrypted, so avoid it on a shared device. Files you save contain the plan details you entered; protect them like other financial records.

Important assumptions before planning around these numbers
  • Returns are applied as a smooth monthly rate. Real markets lurch — the order of good and bad years (sequence risk) matters, especially near withdrawals. Treat the range, not the middle line, as the honest picture.
  • Deposits land at the start of their month, then that month's growth applies.
  • Taxes, fees, and fund expense ratios are not modeled; a 1% annual fee quietly behaves like a 1% lower return.
  • "Raise yearly" compounds each contribution on the anniversary of its first deposit.
  • The today's-dollars view deflates by your single inflation assumption; actual inflation varies.
  • This tool illustrates arithmetic; it is not investment advice or a prediction.

The crossover point is the whole story

Early on, your balance is basically just your deposits — compounding feels like a myth. The tile above marks the month where lifetime growth passes lifetime deposits: from then on, the market has contributed more than you have. Almost everyone who quits investing quits before that point, because the first years look so unimpressive. Seeing the date printed —your date, from your numbers — is the best argument for boring consistency we know of.

Why the "cost of waiting" tile is so brutal

Delaying a plan doesn't trim its final value proportionally — it deletes the last years of compounding, which are the biggest ones. Waiting 5 years out of 40 often costs a third of the final balance. If you can only remember one thing from this page: the amount matters less than the start date. Start with whatever you have.