Financial calculator

Comprehensive Budgeting & Savings Capacity Tool

Simulate household cash flow with monthly income, recurring expenses, rare shocks, scheduled one-time costs, and monthly investment growth. The chart shows percentile bands across many Monte Carlo runs.

Dollar inputs accept commas, like 95,000. Percentage inputs accept values like 6 for 6%. Income inputs are gross before tax, and job-loss events temporarily zero the linked income stream.

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General Assumptions

Set the projection horizon, initial savings, Monte Carlo size, and optional sample-path output. Use annual inputs if your source data is not monthly; recurring cash-flow fields will be converted internally for the simulation.

When enabled, recurring dollar inputs are shown as annual values. Balances like starting savings stay as one-time dollar amounts.

Each month is simulated individually.

Higher counts smooth the percentile lines.

Initial cash available to the household.

Leave blank for fresh random draws. Enter a number to reproduce the same results later.

Optional API sample paths, capped at 5. Leave at 0 to skip them.

Income Streams

Each enabled income stream is sampled from a lognormal distribution every month. Enter gross income before tax, then set a tax rate so the simulator can convert it to net cash flow.

Income rows are before tax. Taxes are applied to the sampled gross income after each draw.

Recurring Expenses

Recurring expenses can be normal or lognormal, and normal draws are floored at zero. The field labels switch between monthly and annual amounts with the input-frequency toggle.

Use lognormal for categories that should never go negative.

Rare Events

Rare events are checked monthly. Expense shocks add cost, while job-loss shocks set income to zero for a duration.

Expense events use dollars. Job-loss events use months for the duration fields.

Scheduled One-Time Expenses

These occur in a specific month and are sampled once for each simulation path. The amount fields follow the current monthly or annual input mode.

Use this for planned repairs, relocations, tuition, or other known future costs.

Investment Returns

Returns are sampled monthly using the annual mean and standard deviation as the reference inputs.

Enter 6 for a 6% annual expected return.

Enter 15 for a 15% annual standard deviation.

The chart and summary update in the browser after the API run completes.

Results

Percentile bands show the spread of projected savings balances.

Waiting for simulation

Summary

Run a simulation to see the projected savings outlook.

Median ending balance
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10th percentile ending balance
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Probability of going broke
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Probability of ending below zero
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Ending Balance Table

Run the simulation to populate the percentile table.

Percentile Ending balance
Run the simulation to see ending balances.