The YoCalc Blog
Plain-English guides to the math behind money, health, and everyday decisions — each paired with a free calculator.
6 min read · Jun 2, 2026
How to Calculate Loan Payments (Step by Step)
Learn how to calculate monthly loan payments by hand with the amortization formula, worked examples, and tips to pay less interest.
Read the guide →7 min read · Jun 9, 2026
Compound Interest: The Complete Beginner's Guide
What compound interest is, how the formula works, and why starting early beats investing more. Includes worked examples and the Rule of 72.
Read the guide →5 min read · Jun 16, 2026
Salary to Hourly: What Your Annual Pay Really Means
How to convert an annual salary to an hourly rate, common salary-to-hourly benchmarks, and why your real hourly rate may be lower than you think.
Read the guide →6 min read · Jun 23, 2026
BMI Explained: What Your Number Means (and What It Doesn't)
How BMI is calculated, what the categories mean, where BMI falls short, and better metrics to track alongside it.
Read the guide →5 min read · Jun 30, 2026
Tipping in 2026: How Much, When, and the Fast Mental Math
How much to tip at restaurants, bars, and for delivery, how to split a bill fairly, and mental math tricks to calculate any tip in seconds.
Read the guide →6 min read · Jul 7, 2026
ROI Made Simple: How to Measure Any Investment's Return
How to calculate return on investment, why annualized return (CAGR) matters more than total ROI, and the costs people forget to include.
Read the guide →5 min read · Jul 14, 2026
Percentage Change Explained: Why 50% Off Then 50% Off Isn't 100% Off
The correct percentage change formula with worked examples, plus why a 50% increase followed by a 50% decrease never gets you back to where you started.
Read the guide →5 min read · Jul 21, 2026
How Stacked Discounts Really Work (And Why They're Smaller Than They Sound)
How to calculate the real savings from stacked discounts and coupon codes, with the math retailers don't spell out for you.
Read the guide →5 min read · Jul 28, 2026
How to Count Days Between Two Dates (And Why the Answer Isn't Always Obvious)
How to correctly count the days, weeks, or months between two dates, including the inclusive/exclusive counting mistake almost everyone makes once.
Read the guide →4 min read · Aug 4, 2026
How to Calculate Your Exact Age in Years, Months, and Days
The correct way to calculate age in years, months, and days from a birth date, including how leap years and month-length differences are handled.
Read the guide →5 min read · Aug 11, 2026
Metric to Imperial Conversion: The Only Cheat Sheet You Need
Practical metric-to-imperial conversion benchmarks and mental math shortcuts for length, weight, and temperature — plus why the official factors are exact.
Read the guide →6 min read · Aug 18, 2026
How GPA Is Calculated (And How to Raise It Strategically)
How grade point average is actually calculated on the 4.0 scale, why credit hours matter more than most students realize, and how to raise a GPA efficiently.
Read the guide →5 min read · Aug 25, 2026
The Real Cost of a Road Trip: Budgeting for Gas Beyond the Estimate
How to budget realistically for a road trip's fuel cost, why your actual mileage rarely matches the sticker rating, and what else to factor in beyond gas.
Read the guide →6 min read · Sep 1, 2026
15-Year vs. 30-Year Mortgage: What the Math Actually Says
A side-by-side breakdown of 15-year vs. 30-year mortgage math: monthly payment, total interest, and the real trade-off between them.
Read the guide →5 min read · Sep 8, 2026
Compound Interest Works Both Ways: Why It's Brutal on Debt
The same compound interest math that grows savings also grows debt — how minimum payments on high-interest debt can barely dent the balance, and what actually pays it down.
Read the guide →6 min read · Sep 15, 2026
Why Your Freelance Hourly Rate Needs to Be Higher Than You Think
Why a freelance hourly rate needs to be well above the equivalent employee salary rate, and how to calculate a rate that actually accounts for unbillable time and costs.
Read the guide →4 min read · Sep 22, 2026
Counting Down to a Future Date: The Math Behind 'X Days Until'
How to calculate the exact number of days until any future date, why 'days until' and 'days between' aren't quite the same question, and common countdown mistakes.
Read the guide →5 min read · Sep 29, 2026
APR vs. Interest Rate: The Difference That Actually Costs You Money
Why a loan's APR and its interest rate are two different numbers, what APR actually includes, and why comparing loans by interest rate alone can be misleading.
Read the guide →4 min read · Oct 6, 2026
Reverse Percentages: How to Find the Original Price Before a Discount or Increase
How to work backward from a final price to the original amount before a percentage increase or decrease was applied, including the VAT-removal case people search for most.
Read the guide →5 min read · Oct 13, 2026
Cooking Measurement Conversions: Why Grams Beat Cups, Plus Oven Temperatures
Why cup measurements aren't reliable for baking, the real gram weights for common ingredients, and how to convert oven temperatures between Fahrenheit and Celsius.
Read the guide →5 min read · Oct 20, 2026
How Much to Tip: A Guide by Service (Hair, Movers, Delivery, Hotels & More)
Tipping norms for hairdressers, movers, hotel housekeeping, food delivery, and other services beyond the restaurant table, with the reasoning behind each range.
Read the guide →5 min read · Oct 27, 2026
Waist-to-Height Ratio vs. BMI: Which One Should You Actually Track?
How waist-to-height ratio compares to BMI for assessing health risk, why researchers increasingly favor it, and how to use both numbers together instead of picking one.
Read the guide →4 min read · Nov 3, 2026
How to Convert Your GPA to a 100-Point Percentage Scale (and Back)
See exactly how a 3.5 GPA converts to 87.5% (and back) — plus the formula for any scale: 4.0, 4.3, or 5.0, with a worked example both directions.
Read the guide →4 min read · Nov 10, 2026
ROI vs. ROAS: What's the Difference (and Which One Should You Use)?
The difference between ROI and ROAS, why they can tell completely different stories about the same campaign, and when to use each one.
Read the guide →4 min read · Nov 17, 2026
Discount Then Tax, or Tax Then Discount? The Order That Actually Saves You Money
Sales tax should be calculated on the discounted price, not the original — see the exact math with a worked $150 example, and when coupons change the order.
Read the guide →5 min read · Nov 24, 2026
EV vs. Gas: Comparing the Real Cost Per Mile
How to compare the true cost per mile of driving an electric car versus a gas car, with real benchmark numbers for both fuel and home charging.
Read the guide →3 min read · Dec 1, 2026
How to Calculate the Age Gap Between Two People
Find the exact age gap between any two people in years, months, and days from their birth dates — with a simple trick using a standard age calculator.
Read the guide →4 min read · Dec 8, 2026
APY vs. Interest Rate: Why Your Savings Account Earns More Than the Advertised Rate
Why a savings account's APY is always slightly higher than its stated interest rate, what compounding frequency has to do with it, and why APY is the number to compare.
Read the guide →5 min read · Dec 15, 2026
Cash-on-Cash Return: How to Measure a Rental Property's Real Yield
How to calculate cash-on-cash return for a rental property, why it's different from total ROI, and what counts as a good number in 2026.
Read the guide →4 min read · Dec 22, 2026
How to Calculate Overtime Pay (Time-and-a-Half, Explained)
How to calculate time-and-a-half overtime pay from an hourly rate or a salary, including the base rate you actually need to start from.
Read the guide →4 min read · Dec 29, 2026
How to Split a Restaurant Bill Unevenly (When Everyone Ordered Differently)
How to split a bill fairly when people ordered very different amounts, including the tip, instead of dividing everything evenly by headcount.
Read the guide →4 min read · Jan 5, 2027
Markup vs. Margin: Why a 50% Markup Isn't a 50% Margin
The difference between markup and margin, why they use different formulas even though they're both about the same profit dollar amount, and how to convert between them.
Read the guide →4 min read · Jan 12, 2027
Buy One Get One (BOGO) vs. a Flat Percentage Off: Which Actually Saves More?
Whether 'buy one get one free' or 'buy one get one 50% off' saves more than an equivalent-sounding flat percentage discount, worked out with real numbers.
Read the guide →4 min read · Jan 19, 2027
How to Calculate Business Days Between Two Dates
How to calculate the number of business days (excluding weekends and holidays) between two dates, with the formula and a worked example.
Read the guide →4 min read · Jan 26, 2027
The Real Annual Cost of Your Commute (Beyond Just Gas)
How to calculate the true yearly cost of a daily commute from your one-way distance, and what else besides gas belongs in that number.
Read the guide →4 min read · Feb 2, 2027
Ideal Body Weight (Devine Formula) vs. BMI: Two Different Ways to Estimate a Healthy Weight
How the Devine formula for ideal body weight works, how it differs from BMI's healthy weight range, and why hospitals use it for medication dosing.
Read the guide →4 min read · Feb 9, 2027
Corrected Age for Premature Babies, Explained (With the Formula)
How to calculate a premature baby's corrected (adjusted) age from their chronological age and how many weeks early they were born, and why doctors use it.
Read the guide →3 min read · Feb 16, 2027
Height Conversion: Feet and Inches to Centimeters (and Back)
How to convert height between feet/inches and centimeters, with the exact formula and common benchmark heights already worked out.
Read the guide →5 min read · Feb 23, 2027
How to Calculate Weighted GPA (AP, IB, and Honors Bonus Points)
How weighted GPA adds bonus points for AP, IB, and Honors courses, the common weighting scales schools use, and why colleges often strip the bonus back out.
Read the guide →4 min read · Mar 2, 2027
How Extra Payments Reduce Total Loan Interest
How extra principal payments cut total loan interest and shorten a loan's term, with a technique for estimating the savings using a standard loan calculator.
Read the guide →3 min read · Mar 9, 2027
The Rule of 72, Explained (With Real Examples)
How the Rule of 72 estimates how long it takes money (or debt) to double at a given interest rate, with worked examples across investing, debt, and inflation.
Read the guide →4 min read · Mar 16, 2027
Which Home Renovations Actually Have the Best ROI?
Which home improvement projects return the most value relative to their cost, with real percentage figures for garage doors, kitchens, and other common renovations.
Read the guide →3 min read · Mar 23, 2027
How Many Work Hours Are in a Year? (2,080 and the Real-World Adjustments)
Why 2,080 is the standard number of work hours in a year, how holidays and PTO change your real total, and why the exact number shifts slightly year to year.
Read the guide →4 min read · Mar 30, 2027
Tipping Around the World: Where It's Expected and Where It's Rude
Which countries expect a tip, which build service into the price already, and where tipping can actually cause offense — a practical guide before you travel.
Read the guide →3 min read · Apr 6, 2027
Price Per Unit: How to Tell Which Size Is Actually the Better Deal
How to calculate price per unit to compare different package sizes fairly, and why the bigger size isn't always the cheaper one per unit.
Read the guide →3 min read · Apr 13, 2027
Dog Age in Human Years: The Real Formula (Not Just ×7)
The science-backed formula for converting a dog's age to human years, why the old multiply-by-seven rule is wrong, and a worked example.
Read the guide →3 min read · Apr 20, 2027
How to Calculate a Salary Raise Percentage
How to calculate the percentage of a raise from your old and new salary, plus what counts as a good raise in 2026.
Read the guide →4 min read · Apr 27, 2027
How to Calculate Your Pregnancy Due Date
How to calculate an estimated due date from the first day of your last menstrual period, why it's 280 days, and why an ultrasound date can differ.
Read the guide →3 min read · May 4, 2027
How to Calculate Your Car's Real MPG From a Fill-Up
How to calculate your car's actual fuel economy from a full tank of gas, and why it's usually lower than the EPA sticker number.
Read the guide →3 min read · May 11, 2027
BMI for Kids and Teens: Why the Adult Formula Doesn't Apply
Why children and teens need age- and sex-specific BMI percentiles instead of the fixed adult BMI categories, and where to find the right calculator.
Read the guide →3 min read · May 18, 2027
Miles to Kilometers for Runners: 5K, 10K, and Marathon Distances
Quick mile-to-kilometer conversions for common race distances, plus how to convert your own pace between min/mile and min/km.
Read the guide →3 min read · May 25, 2027
What GPA Do You Need for Cum Laude, Magna, or Summa?
Typical GPA requirements for cum laude, magna cum laude, and summa cum laude graduation honors, and why the exact cutoff varies by school.
Read the guide →4 min read · Jun 1, 2027
Car Loan vs. Lease: Which Actually Costs Less?
Whether financing or leasing a car is cheaper, comparing monthly payments, total cost over time, and who each option actually makes sense for.
Read the guide →3 min read · Jun 8, 2027
How Much to Tip DoorDash and Uber Eats Drivers
How much to tip food delivery drivers on DoorDash, Uber Eats, and similar apps, and why the app's delivery fee doesn't go to your driver.
Read the guide →3 min read · Jun 15, 2027
How Many Years Until You Can Retire? A Simple Countdown
How to calculate exactly how many years, months, and days remain until a target retirement age using nothing but a birth date and a target date.
Read the guide →