6 Money Rules They Don’t Teach in School (But You Need by Age 30)

We grow up learning algebra and grammar, but somehow, schools skip some of the most essential life lessons, like how to manage money. Most people graduate with little to no knowledge of how to budget, invest, or even open a retirement account. If you’ve entered your 20s feeling overwhelmed by personal finance, you’re not alone.

By the time you reach your 30s, though, it’s time to take the wheel. These six foundational money rules are simple to understand, powerful in impact, and easy to implement, even if you’re starting from scratch. Whether you're trying to escape paycheck-to-paycheck living or build long-term wealth, this is your roadmap to financial confidence.

Rule #1: The Budget Rule – 50/30/20

The 50/30/20 budget rule is a beginner-friendly framework that helps you make smarter decisions about your income. It breaks your monthly income into three categories:

●  50% Needs: Rent, mortgage, utilities, groceries, insurance, and other essentials.

● 30% Wants: Streaming services, eating out, hobbies, and lifestyle upgrades.

● 20% Goals: Savings, retirement contributions, debt repayments, and investments.

This structure allows you to live within your means while still enjoying life and preparing for the future. It also prevents “lifestyle creep” when your spending grows with your income without improving your financial security.

💡Tip: Automate your savings and debt repayments so that money moves out of your checking account the moment you get paid.

Rule #2: The 72 Rule, How Fast Will Your Investments Double?

The Rule of 72 is a mental math shortcut that estimates how long it takes for your money to double at a fixed annual rate of return.

Formula: 72 ÷ interest rate = years to double your investment

Example: If your investment earns 8% per year: 

72 ÷ 8 = 9 years to double your money.

It’s not just a party trick, it’s a great way to visualize how compound interest works. Whether you're comparing a Roth IRA, high-yield savings account, or index funds, this rule helps you grasp long-term growth.

⚠️ Heads-up: Investments with higher returns tend to carry more risk. Always weigh your options based on your risk tolerance and financial goals.

Rule #3: The Emergency Fund Rule ; Save 3 to 6 Months of Expenses

An emergency fund protects you from life’s financial surprises and keeps you from going into debt when things go wrong. Aim to save 3 to 6 months of living expenses in a liquid, easily accessible account.

Real Emergencies:

●      Unplanned medical expenses

●      Major car repairs

●      Job loss or reduced hours

●      Emergency travel

●      Vet bills for your pet

Avoid the temptation to treat it as a “fun” fund. It’s there for true emergencies not for concert tickets or last-minute vacations.

✅ Pro Tip: Start by saving just one month of expenses. Add to it every paycheck, even $25 a week adds up over time.

Rule #4: The 300 Rule – Your Retirement Number

Ever wonder how much money you need to retire comfortably? The 300 Rule gives you a ballpark estimate.

Formula: Monthly expenses × 300 = Target retirement savings

Example: If your monthly expenses are $4,000: $4,000 × 300 = $1.2 million retirement goal

This is based on the widely used 4% withdrawal rate, meaning you can safely withdraw 4% of your nest egg each year without running out of money.

🧓 Consider these factors:

●      Will your mortgage be paid off?

●      Do you plan to travel?

Will you rely on Social Security, pensions, or rental income?

Rule #5: The New Car Rule – 20/4/10

Cars can be financial traps if you're not careful. The 20/4/10 Rule helps you avoid overcommitting on a car loan.

The Rule:

●      20% down payment

●      4 years max loan term

●      10% or less of your gross income for your monthly car payment

Example:

Income: $60,000/year → $5,000/month gross

Max car payment: $500/month

Loan length: No more than 4 years

Minimum down payment: $6,000 on a $30,000 vehicle

🚘 Why it matters: A car’s value drops fast, often 20% in the first year. This rule keeps you from overspending and going “upside down” on your loan.

Rule #6: The Rent Rule : 3x Income

Housing is likely your biggest monthly expense, so keeping it manageable is key to your financial stability. The general rule of thumb? Your rent should be no more than 1/3 of your gross monthly income.

Formula: Monthly income ÷ 3 = Max affordable rent

Example: If you earn $3,600/month gross, your rent should be no more than $1,200/month.

📍 If that’s unrealistic where you live, consider:

●      Living with roommates

●      Relocating further from city centers

● Negotiating rent or looking into housing assistance

Conclusion: It’s Okay to Learn Late, Just Don’t Learn Too Late

Most people don’t graduate school knowing how to file taxes, build an emergency fund, or estimate how much they’ll need to retire. If this is your first time hearing these rules, you’re actually ahead of the game, because you’re actively choosing to get financially informed.

These six money rules are your foundation. They won’t solve everything overnight, but following them can set you up for financial stability, reduce stress, and help you reach your long-term goals, from owning a home to retiring early.