Unit 3: Budgeting and Saving

Last updated 10/14/2026 by

Andrew Latham

Summary:

A budget decides in advance where your money goes, so less of it leaks away on things you would not have chosen. People who track their spending and save automatically are far better prepared for surprises.

This is Unit 3 of 9 in Money 101 by SuperMoney, a free personal finance course. It takes about 2.5 weeks in a classroom, or 45 to 90 minutes on your own. Then take the five-question quiz below. Score 4 of 5 to mark the unit complete.

What you’ll learn

Track spending for two weeks and sort it into needs, wants and saving.
Build a monthly budget from a real income figure.
Plan for fixed, variable and irregular expenses.
Size an emergency fund and explain where to keep it.
Set a SMART savings goal and automate progress toward it.
Calculate compound interest and use the rule of 72.
Recognize common behavioral spending traps.

Key terms

Budget: A plan for every dollar of income: what you will spend, save and give.
Fixed expense: A cost that stays the same each month, such as rent or a phone plan.
Variable expense: A cost that changes month to month, such as groceries or gas.
Irregular expense: A cost that does not come every month but is predictable over a year, such as car repairs, gifts or annual subscriptions.
Sinking fund: Money set aside a little each month for an irregular expense.
Emergency fund: Savings for true surprises, such as a job loss or medical bill. A common target is three to six months of essential expenses.
Pay yourself first: Moving money to savings automatically on payday, before you spend.
Compound interest: Earning interest on your interest, so growth speeds up over time.
Rule of 72: Divide 72 by an interest rate to estimate how many years it takes money to double.

Lesson 3.1: Where does the money go?

Before you can plan spending, you need to know what it looks like now. For two weeks, write down every purchase, including small ones and subscriptions that renew automatically. Bank and card apps can help, but cash and app purchases are easy to miss.

Sort each purchase into three groups. Needs are costs you must pay to live and work: housing, basic food, transportation, insurance, minimum debt payments. Wants make life better but are optional: eating out, entertainment, upgrades. Saving is money set aside for the future. Many things are partly both. A phone is a need, but the newest model is a want.

Lesson 3.2: Building a budget that works

A simple starting point is the 50/30/20 guideline: about 50% of take-home pay to needs, 30% to wants and 20% to saving and extra debt payments. Adjust it to fit your life. In high-rent areas needs may take 60% or more, and that is fine if you adjust wants.

Budgets fail most often because of irregular expenses. Car repairs, birthday gifts, annual subscriptions and back-to-school costs come every year, just not every month. Add them up, divide by 12, and save that amount monthly in a sinking fund.

Use whatever method you will actually keep: a spreadsheet, an app, separate bank accounts for different goals, or envelopes of cash. Whichever you pick, look at it once a week.

Lesson 3.3: Saving on autopilot

Your first savings goal is an emergency fund. Start with a mini goal such as $500 or $1,000, which covers most small emergencies. Then build toward three to six months of essential expenses. Keep it in a separate, insured, high-yield savings account: easy to reach in an emergency, but not linked to your debit card.

Set goals the SMART way: specific, measurable, achievable, relevant and time-bound. “Save more” is a wish. “Save $1,200 for a used laptop by June by moving $100 every payday” is a plan.

Then pay yourself first. Set an automatic transfer to savings for the day after payday. People save far more when saving is the default instead of a decision they make every month.

Lesson 3.4: Compound interest and money habits

Compound interest means you earn interest on your interest. $1,000 earning 5% a year becomes $1,050 after one year, then $1,102.50 after two, because the second year’s interest is calculated on $1,050. Over decades, compounding does most of the work.

The rule of 72 estimates doubling time: divide 72 by the annual rate. At 6%, money doubles in about 12 years. At 9%, about 8 years. The same rule works against you on debt: a card balance at 24% doubles in about 3 years if you do not pay it down.

Watch for habits that quietly undo a budget: lifestyle creep (spending rises every time income does), forgotten subscriptions, spending to keep up with friends, and the “it’s only $5” trap. $5 a day is more than $1,800 a year.

Worked example: a first-job budget

Assumes $38,000 salary and about $2,600 a month take-home after taxes and benefits. Rent varies a lot by area; use real local listings in the activity.

Take-home pay	$2,600
Needs: rent with roommate, utilities, groceries, transportation, insurance, phone	$1,430 (55%)
Wants: eating out, entertainment, clothes, subscriptions	$650 (25%)
Saving: emergency fund, sinking funds, retirement	$520 (20%)

Takeaway: At $520 a month, this person has a $3,000 starter emergency fund in under six months and can then shift money to longer-term goals.

Activity: Two-week tracker and first-year budget

Part 1: Track every purchase for two weeks and sort it into needs, wants and saving. Part 2: Build a monthly budget for a first job paying $38,000 a year in your area, using real rent from local listings. Include at least three irregular expenses as sinking funds.

Total spent in two weeks: needs, wants, saving
Your biggest surprise from tracking
Monthly take-home pay used for Part 2
Rent you found and where you found it
Three irregular expenses and their monthly sinking fund amounts
Your emergency fund goal and how many months to reach it

The printable worksheet and the sample documents for this activity are in the Money 101 course book (PDF).

Reflect: Which of your spending habits would be hardest to change, and what is one small step you could take this month?

Up next: Unit 4: Credit Reports, Scores and Credit Cards | Previous: Unit 2: Banking and Payment Tools | Course overview

Andrew Latham

Andrew is the Content Director for SuperMoney, a Certified Financial Planner®, and a Certified Personal Finance Counselor. He loves to geek out on financial data and translate it into actionable insights everyone can understand. His work is often cited by major publications and institutions, such as Forbes, U.S. News, Fox Business, SFGate, Realtor, Deloitte, and Business Insider.

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