Budget for timing and surprises
Can a plan with ordinary monthly surplus still run out of cash?
Start with a concrete question
An original fictional budget starts with 100 credits. Income, fixed spending and variable spending recur for three months; an extra expense arrives in month two.
Try the initial inputs, then write a prediction before changing one setting. All calculations run locally on your CPU.
What do you expect?
Predict whether a larger month-two expense changes only that month’s final cash.
Change one thing. Inspect what happens.
- Calculate the ordinary monthly surplus at defaults.
- Increase the surprise until the lowest balance becomes negative.
- Find a reserve or spending adjustment that keeps every month funded, not only the final month.
Your settingsMechanism
Calculation belowEvidence
Compare outcomes
Compare the current results
Every bar starts at zero and uses the same numeric scale in this chart. The upper bound automatically adjusts to the largest current value (at least 1), so compare the numbers when changing inputs. Units and quantities come from each label; different kinds of quantity are not interchangeable. Displayed values are rounded to at most six significant digits.Follow the calculation
- Month 1: income 300 − fixed 180 − variable 80 − surprise 0; ending cash 140.
- Month 2: income 300 − fixed 180 − variable 80 − surprise 60; ending cash 120.
- Month 3: income 300 − fixed 180 − variable 80 − surprise 0; ending cash 160.
An average surplus does not guarantee enough cash at every date. Negative cash is a funding gap, not permission to borrow.
Captures keep your inputs, prediction and observation. Results are recalculated from those inputs. Resetting inputs keeps your captures and challenge history.
Explain the mechanism
Budget for timing and surprises
An original fictional budget starts with 100 credits. Income, fixed spending and variable spending recur for three months; an extra expense arrives in month two.
Predict before changing inputs
Predict whether a larger month-two expense changes only that month’s final cash.
Understand the mechanism
A budget compares inflows and outflows; a cash-flow plan also tracks when they occur.
Defaults leave 40 credits per ordinary month. Cash goes 100→140→120→160 because month two includes an extra 60.
A negative balance means the plan needs funding or changed spending. The model reports a funding gap without assuming access to borrowing.
Calculate it yourself
Next cash = previous cash + income − fixed spending − variable spending − surprise expense.
Guided investigation
Calculate the ordinary monthly surplus at defaults.
Increase the surprise until the lowest balance becomes negative.
Find a reserve or spending adjustment that keeps every month funded, not only the final month.
Assumptions and limitations
Fictional credits, fixed income and only three months; taxes and real borrowing terms are omitted.
This is arithmetic practice, not personal financial advice.
Further investigations
High school: Create a fictional event cash plan and a contingency reserve.
College: Model variable income and compare minimum balance with average surplus.
Working professionals: Prepare a departmental cash forecast with explicit timing assumptions.
Try a fresh case
Start with 50 credits; monthly income 100 and spending 80. A 30-credit surprise occurs in month two. What is cash after two months?
This is a public practice check. Retries support learning; matching a number does not certify independent proficiency.
Take the investigation further
Choose any extension. These are project prompts for you to carry out; they are not automatically assessed.
School investigation
Create a fictional event cash plan and a contingency reserve.
College investigation
Model variable income and compare minimum balance with average surplus.
Workplace investigation
Prepare a departmental cash forecast with explicit timing assumptions.
Keep the evidence, choose your next step
Completion records your own decision that you have worked through this investigation. Practice checks and independent project evidence are separate.