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Budget Planning Math Project
Grades 7-12 · 1 week
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A monthly budget is a plan for how money will be earned, spent, saved, and set aside over one month. For a first job, budgeting helps students connect math skills to real choices like transportation, phone bills, food, and entertainment. It also shows that income is limited, so every spending category needs a realistic amount. A budget dashboard makes these choices visible with totals, percentages, charts, and checklists.
The basic method is to start with net income, subtract fixed expenses, estimate variable expenses, and then assign money to savings and sinking funds. Percentages such as the 50/30/20 rule help compare spending to a recommended balance of needs, wants, and savings. Pie charts, bar graphs, and tables can show whether the plan is balanced or if one category is too large. When the numbers do not fit, students revise the plan by reducing wants, adjusting savings goals, or finding ways to increase income.
Key Facts
- Net income = gross income - deductions
- Total expenses = fixed expenses + variable expenses + savings + sinking funds
- Money left over = net income - total expenses
- Percent of income = category amount / net income × 100%
- 50/30/20 rule: 50% needs, 30% wants, 20% savings and debt repayment
- Monthly sinking fund amount = future cost / number of months until payment
Vocabulary
- Net income
- Net income is the amount of money left from a paycheck after taxes and other deductions are removed.
- Fixed expense
- A fixed expense is a cost that stays about the same each month, such as rent, a phone plan, or a bus pass.
- Variable expense
- A variable expense is a cost that can change from month to month, such as food, clothing, or entertainment.
- Savings
- Savings is money set aside for future goals, emergencies, or large purchases instead of being spent right away.
- Sinking fund
- A sinking fund is a small monthly amount saved for a known future expense, such as a school trip or yearly subscription.
Common Mistakes to Avoid
- Using gross income instead of net income, which makes the budget look like there is more spendable money than there really is.
- Forgetting irregular expenses, which causes the plan to fail when yearly fees, gifts, repairs, or school costs appear.
- Treating savings as whatever is left over, which often leads to saving nothing because spending fills the whole budget.
- Adding percentages without checking the dollar amounts, which is wrong because a category can look reasonable as a percent but still be unaffordable in the actual budget.
Practice Questions
- 1 A student earns $14 per hour and works 18 hours per week for 4 weeks. If deductions are 12% of gross pay, what is the student's monthly net income?
- 2 A monthly net income is 410, variable expenses are 180, and sinking funds are $95. Find the money left over and the percent of income used for savings.
- 3 A student's budget follows the 50/30/20 rule, but their wants category is too high because of streaming, snacks, and weekend spending. Explain two changes they could make while still keeping the budget realistic.