# Cash runway calculator: how long will money last? documentation

Inputs, formulas, assumptions and API/MCP examples for the cash runway calculator: how long will money last?. Reproduce a calculation and cite its sources.

Canonical calculator: https://klarfort.com/tools/runway-calculator/
Content updated: 2026-09-07
Assumptions reviewed: 2026-09-07

## Overview
Estimate how many months your liquid savings can cover the gap between recurring income and expenses. Compare your current cash flow with lower spending, higher income and a stress scenario.

Separate modes model a complete loss of recurring income, the funding needed for a sabbatical or varying monthly cash flows. This calculator models cash coverage without investment returns.

## How to use
1. Enter liquid savings, recurring monthly income and recurring monthly expenses in one currency.
2. Add obligations due over the next 12 months only if they are not already included in monthly expenses.
3. Choose the mode and scenario. Enter leave details for a sabbatical or horizon, variation and path settings for drawdown.
4. Calculate and compare runway, monthly cash burn and the scenario table or simulated balance range.

## Understanding the result
Cash burn is the monthly gap that savings must cover. The scenario result divides liquid savings by that gap, with a 999-month display cap when coverage is very long or there is no modeled depletion.

Runway states are Secured at 12 months or more, Building from 6 to under 12, On watch from 3 to under 6 and Critical below 3. These labels describe the modeled duration; drawdown uses its horizon-capped median.

## Questions
### What changes in the four scenarios?
Current keeps recurring income and spending unchanged. Trim Spending reduces spending by 10%. Raise Income increases income by 15%. Stress reduces income by 15% and raises spending by 10%. Separate obligations are not multiplied.

### How does job loss differ from a sabbatical?
Job-loss mode sets recurring income to zero. Sabbatical mode uses your entered income during leave and reports cash needed, cash after leave and any funding shortfall for its chosen length.

### How are one-year obligations and drawdown risk handled?
The simple runway ratio spreads obligations over 12 months as part of the monthly gap. Sabbatical funding and drawdown include that finite bucket only in the first 12 months. Drawdown varies recurring income and expenses and counts any month-end balance at zero or below as ruin.

## Default worked example
Months of runway: 12 months. Estimated runway under current assumptions. Assumptions as of 2026-09-07.

## Formula
Burn = max(expenses × expense factor + obligations ÷ 12 − income × income factor, 0). Runway = min(savings ÷ burn, 999).

- Current keeps income and spending unchanged. Trim Spending reduces spending by 10%; Raise Income increases income by 15%; Stress reduces income by 15% and raises spending by 10%.
- Separate obligations are spread over 12 months and are never multiplied. Do not include the same amount in recurring expenses.
- Runway follows the app: two-decimal half-up rounding and a 999-month cap. Zero burn is shown as 999, with no depletion under the stated assumptions.
- Drawdown uses independent monthly income and expense shocks; it includes no investment returns. A simulated probability depends on the assumptions and is not a prediction.
- Drawdown and sabbatical funding spread entered due obligations over the first 12 months only. Later months exclude that finite obligation bucket.
- Dashboard states follow displayed runway: Secured at 12 months or more, Building at 6 to under 12, On watch at 3 to under 6, Critical below 3. Drawdown applies these labels to its horizon-capped simulated median duration.

## Inputs
- currency: All entered amounts use this currency. No automatic currency conversion.; default "USD"
- mode: Mode; default "scenarios"
- scenario: Scenario; default "current"
- liquidAssets: Liquid savings; default 12000
- monthlyIncome: Recurring monthly income; default 2000
- monthlyExpenses: Recurring monthly expenses; default 3000
- obligationsDue12Months: Separate obligations due over 12 months; default 0
- leaveMonths: Sabbatical length in months; default 6
- incomeDuringLeave: Monthly income during leave; default 0
- horizonMonths: Simulation horizon in months; default 120
- variancePercent: Monthly income and expense variation (%); default 10
- paths: Simulation paths; default 1000
- seed: Simulation seed; default ""

## Interfaces
Input schema: https://klarfort.com/tools/runway-calculator/schema.json
Worked request and response: https://klarfort.com/tools/runway-calculator/examples.json
Public table: https://klarfort.com/tools/runway-calculator/table.json
JSON API: POST https://klarfort.com/tools/api/v1/runway-calculator
MCP endpoint: POST https://klarfort.com/tools/mcp
MCP tool name: runway-calculator

## JSON request body
```json
{
  "currency": "USD",
  "mode": "scenarios",
  "scenario": "current",
  "liquidAssets": 12000,
  "monthlyIncome": 2000,
  "monthlyExpenses": 3000,
  "obligationsDue12Months": 0,
  "leaveMonths": 6,
  "incomeDuringLeave": 0,
  "horizonMonths": 120,
  "variancePercent": 10,
  "paths": 1000,
  "seed": "6d43b8fa7170a06d"
}
```

## Usage and credit
Free for personal, commercial and any other lawful use with credit to KlarFort at https://klarfort.com/. Third-party data terms still apply.

Computed with KlarFort Calculators, https://klarfort.com/

Place a visible credit near the reused material or in the credits for your work or integration. One clear credit per work or integration is sufficient; no separate credit per API request is required. The credit_url field contains the homepage. The citation_url field is an optional calculator reference. Full permission: https://klarfort.com/tools/docs/license/

## Sources
KlarFort shared business rules and RunwayMath: https://klarfort.com/tools/methodology/ (Shared rules 1, simulation 2)