AskANumber.com

Guides

The questions behind the numbers — is this rate good, how much can I afford, is my payment too high — answered in plain English, each linked to the calculator that runs your figures.

Money
How much house can I afford?
How much house you can afford, explained with the 28/36 rule — a simple way to turn your income, debts, and down payment into a realistic home price and payment.
What is a good mortgage rate?
What counts as a good mortgage rate right now, how it compares to the national average, and how much a fraction of a percent changes your monthly payment.
What's a good interest rate on a car loan?
What a good car loan interest rate looks like, how new- and used-car rates differ, how your credit score moves it, and what the average rate is right now.
Is my student loan payment too high?
How to tell if your student loan payment is too high — the share-of-income rule of thumb, when to worry, and the repayment options that can lower it.
How much should I save each month to retire?
How much to save each month for retirement, from the 15%-of-income rule to the 25x target — and how starting earlier dramatically cuts what you need to set aside.
Should I refinance my mortgage?
When refinancing a mortgage is worth it — the rate-drop rule of thumb, how to find your break-even month on closing costs, and the traps to avoid.
Health
Is a BMI of 27 healthy?
Is a BMI of 27 healthy? Where 27 falls on the WHO scale, what the overweight range means, and why BMI alone doesn't tell the whole story.
What is a healthy body fat percentage?
Healthy body fat percentage ranges for men and women, by category — from essential fat to fitness to obese — and why it's often a better signal than BMI.
How many calories should I eat to lose weight?
How many calories to eat to lose weight: start from your maintenance calories, then subtract a deficit — about 500 a day for roughly a pound a week.
How much water should I drink a day?
How much water to drink a day: the ~3.7 L (men) and ~2.7 L (women) total-water guideline, what counts toward it, and when your needs go up.
What heart rate should I exercise at?
Your target heart rate for exercise: 50–70% of max for moderate effort, 70–85% for vigorous, with max estimated as about 220 minus your age.
How many calories do I burn a day?
How many calories you burn a day (your TDEE): resting metabolism from the Mifflin-St Jeor formula times an activity factor, and why it's your maintenance level.
Everyday Math
How do I calculate a percentage?
How to calculate a percentage: to find X% of a number multiply by X/100; to find what percent one number is of another, divide and multiply by 100.
How do I calculate percentage change?
How to calculate percentage change: subtract the old value from the new, divide by the old value, and multiply by 100 — positive is an increase, negative a decrease.
What is a good GPA?
What counts as a good GPA on the 4.0 scale — 3.0 is a solid B average, 3.5+ is strong — and why 'good' depends on your goal and the scale used.
What grade do I need on my final exam?
The exact score you need on your final: (target − current × (1 − final weight)) ÷ final weight — with what to do when the answer is over 100%.
How much should I tip?
How much to tip: the U.S. 15–20% restaurant standard (18–20% for good service), plus quick norms for bars, taxis, and hotels — and how customs vary abroad.
Dates & Time
How do I calculate my age?
How to calculate your age in years: subtract your birth year from the current year, then subtract one if your birthday hasn't happened yet this year.
How many business days are between two dates?
How to count business days between two dates — weekdays minus weekends and holidays — and why a '5 business day' window can span more than a week.
How many days until a specific date?
How to work out how many days until a future date — count the calendar days from today, mind inclusive vs exclusive counting, and watch for leap days.