Find When A Money Plan Stops Working
Why This MattersSay which cash condition you are testing before finding the point where it fails.
Change the assumptions to find when a stated cash condition fails. This shows a limit in an example, not the chance of a future event.
Say Which Cash Condition You Are Testing
Below a chosen cushion and unable to fund a payment are different results. Decide which question you are asking.
A break-even boundary is where a stated condition is just met. It is not a prediction, a probability of success, or a complete recommendation. Choose the condition first: income covering monthly spending, no payment without funding, staying above a chosen cash minimum, or something else. Different conditions produce different limits even with the same money records.
Consider an invented six-month plan with $8,000 opening cash, $4,000 monthly earned income and $4,500 total monthly cash uses. There is no asset income, new borrowing or other receipt. The household chooses a $3,000 reserve floor. Every amount remains constant except an income reduction beginning in month two. Other consumption and investment transfers continue unchanged. This is deliberately a plan already drawing down cash, not a universally desirable starting position.
Find The Limit In A Simple Example
This example spends more than it earns even before an interruption. The formula tracks how an income loss draws down cash further.
Without an income interruption, monthly cash changes by $4,000 − $4,500 = −$500. Six months therefore leave $8,000 − 6 × $500 = $5,000. Let x be the fraction of earned income lost, between zero and one, and let d be the number of reduced-income months inside this horizon. Each affected month removes another $4,000x, so ending cash is $5,000 − $4,000xd.
Every month has negative cash flow in this example, including months outside the interruption. The cash path therefore decreases throughout, making ending cash its minimum. Preserving the $3,000 floor requires $5,000 − $4,000xd ≥ $3,000, or xd ≤ 0.5. This conclusion depends on the monotone path. It would not follow merely from a positive final balance in a plan that falls and later recovers.
Separate A Cash Cushion From A Shortfall
The same plan can avoid a negative balance while still falling below the cash amount the household chose to protect. Neither result is a universal safety rating.
For a two-month interruption, the floor is maintained only when x ≤ 0.25: at most a 25% reduction under these assumptions. For one month, the boundary is 50%; for three months it is one-sixth, approximately 16.67%. Equality means the modeled minimum touches the chosen floor. Income rounded to cents can move a displayed boundary slightly, so inspect the actual ledger when using an exact amount rather than treating a rounded percentage as authoritative.
Nonnegative cash is a separate, weaker condition. Here it requires $5,000 − $4,000xd ≥ 0, or xd ≤ 1.25. A two-month 50% loss ends at $1,000: no modeled negative balance, but a $2,000 breach of the chosen floor. Calling that plan safe would conceal the policy being tested. Calling it bankrupt would also exceed what the arithmetic establishes. The useful description identifies the exact condition, amount and horizon.
Read The Grid As Examples
A colored cell shows what happens with those inputs. It does not tell you how often that situation will occur.
Each grid cell repeats the calculation with a chosen loss percentage and duration. The author selects those rows and columns; they are not measured frequencies. A larger share of passing cells does not establish a probability of success. Changing the spacing could change that share without changing the household. Use the grid to find where results change and what to investigate.
Inspect neighboring cells near a transition rather than relying only on a color. Note the lowest cash, the first floor breach and the first unfunded month. The interruption begins in month two, so at most five interrupted months fit inside a six-month horizon. A nominal duration extending beyond the horizon cannot be treated as fully observed. Extend the ledger if later months could change the decision, keeping the new assumptions explicit.
Check Every Month When Timing Changes
A later recovery can hide an earlier problem. The ending-balance shortcut works here only because the cash path keeps falling under the stated assumptions.
The simple formula changes if optional spending pauses, asset income changes, an extra cost arrives, or positive months follow the interruption. Each choice changes an amount or its timing. A recovering balance can finish above the chosen minimum after falling below it earlier. Calculate every point in the plan, including the opening cash, before reporting the lowest balance.
The immediate monthly operating break-even in the unshocked example is $4,500 earned income if all other inputs remain fixed. That is different from the six-month reserve boundary because opening cash can temporarily absorb a deficit. Sensitivity analysis helps distinguish a tolerable temporary drawdown from a flow that would continue consuming resources. It cannot establish which sacrifices are acceptable, whether a receipt will arrive on time, or whether the omitted scenarios are unimportant.
The Main Points
- Name the condition before finding its limit.
- The share of passing grid cells is not a probability.
- Use the full cash path unless the assumptions justify checking only the ending balance.
Try This Small Exercise
- Check the chosen-cushion and nonnegative-cash limits for a two-month income interruption.
- Add a $500 payment in month two and work out the new cash-cushion limit.
- Use the tool to inspect neighboring cells where the result changes, then read their monthly records.