Engine-calculated example
Starting with $100,000, adding $10,000 each month, using a 12% nominal rate, and reinvesting for five years produces $1,006,533 in Money Stack. Of that, $700,000 is contributed capital: $100,000 initially and $600,000 over 60 months.
Balanceₘ = (Balanceₘ₋₁ + Contributionₘ) × (1 + r / 12) − Costsₘ
The engine adds a contribution before interest, effectively modelling a beginning-of-month deposit. End-of-month deposits would earn slightly less over the same period.
A contribution you can maintain beats a perfect spreadsheet
Choose an amount that survives an ordinary bad month, not just your best month. If income varies, estimate a conservative baseline and use one-time contributions for genuine surpluses. The Cash Years irregular-income guide helps convert mixed payment frequencies without pretending one-off work is recurring salary.
A practical sequence
- Separate emergency cash and near-term bills.
- Set a sustainable recurring amount.
- Enter known future costs as one-time events.
- Run a lower-rate, lower-contribution stress case.
- Compare ending capital with total contributions.
Starting sooner helps because more contributions receive more periods, but a longer horizon also carries more uncertainty. A higher assumed rate is not a free substitute for a realistic contribution plan.
Investor.gov describes regular investing as contributing a set dollar amount or share of income. Its examples are educational, as is this one; investments do not have a guaranteed rate.