Configure a scenario
- Starting capital. Exclude near-term bills and emergency cash unless they truly belong to this horizon.
- Annual rate. The model divides it by 12 and keeps it constant.
- Interest mode. Withdraw reports interest as cash flow; Reinvest adds it to the balance.
- Monthly events. Contributions enter before interest, costs after it.
- One-time events. Add a known lump-sum contribution or expense in its month.
- Horizon. Compare several lengths rather than only a target date.
Read the outputs correctly
Interest earned is the model's gross interest. Costs are the expenses entered. Ending capital is the remaining balance. Net after costs is interest minus costs; your contributions are not reported as profit. An uncovered shortfall appears when neither interest nor principal can meet an expense.
Calculation order
Each month, the engine rounds money to cents, adds contributions, applies annual rate / 12, then subtracts expenses. The supported horizon is 12 to 360 months. It records the first month when balance reaches zero.
Deliberate limitations
Money Stack does not model changing rates, market volatility, inflation, exchange rates, jurisdiction-specific taxes, percentage fees, early-exit terms, default, or frozen liquidity. A deterministic result is an illustration of inputs, not a probability-weighted forecast.
Scenario settings remain in browser local storage. The app does not request a bank login, account, name, or transaction history.
A safer workflow
Measure cash flow and emergency runway in Cash Years first. Move only genuinely long-term capital into the Money Stack scenario. Save a base and stress version and change assumptions when evidence changes—not merely to improve the answer.
This guide explains the tool. It is not individualized financial, tax, or investment advice.