APR vs Interest Rate vs APY: What Each Number Really Costs You
The interest rate, the APR and the APY on the same loan or account are rarely the same number. Here is what each one includes, with worked examples.
Roth IRA vs 401(k) vs Traditional IRA: 2027 Limits and Which to Choose
The 2027 contribution limits for 401(k)s and IRAs, the core tax tradeoff between Roth and traditional accounts, and a worked example showing when each comes out ahead.
How Much Do I Need to Retire? The 4% Rule, Rule of 72 and Coast FIRE
The 4% rule turns your yearly spending into a savings target. Worked examples show the target, the Rule of 72, Coast FIRE numbers and how Social Security changes the math.
How to Calculate GPA: Semester, Cumulative and Weighted
The 4.0 scale, quality points times credit hours, a full semester example, cumulative GPA, weighted vs unweighted, pass/fail rules and what it takes to raise a GPA.
Mean, Median, Mode and Weighted Average: When to Use Each
Step-by-step mean, median and mode, why a single outlier can wreck an average, weighted averages for grades and prices, trimmed means, and a guide to choosing.
Debt Snowball vs Avalanche: Which Pays Off Debt Faster?
Smallest balance first or highest rate first? A month-by-month comparison on four debts, the interest difference, the Kellogg study on small wins and a plan to start.
Inflation: How It Erodes Savings and How to Calculate It
The CPI percent-change formula with worked examples, adjusting past prices, monthly vs yearly rates, the October 2026 data gap and real returns on savings.
Dog Years to Human Years: The Real Formula, Not × 7
Why × 7 is wrong, the 16 × ln(age) + 31 formula from a 2020 study of Labradors, a full age table, and the AAHA life stages that guide your dog’s care.
How Much Protein Do You Need per Day? By Weight, Age and Goal
The RDA is 46 g for women and 56 g for men (0.8 g/kg). See your amount by weight, the 10–35% calorie range, children, pregnancy and sample days of food.
Calorie Deficit: How to Calculate It and How Big It Should Be
Estimate your calorie needs from the Dietary Guidelines table, choose a sensible deficit for 1 to 2 lb a week, and see worked examples and why progress slows.