Blog & Guides

Master your money with our practical guides to personal finance, investing, and everyday math.

Privacy-First Percentage Calculator: How We Compare to Calculator.net, Omnicalculator, and Calculatorsoup

Published: May 13, 2026

An honest side-by-side of iPercentageCalculator vs. the big three free calculator sites. What each does well, where our model is different, and which to pick.

What is 15% of 200? (Answer + How to Calculate)

Published: May 13, 2026

15% of 200 is 30. Here's the formula, three ways to work it out, and worked examples for tips, discounts, and tax.

What is 20% of 150? (Answer + Quick Mental Math)

Published: May 12, 2026

20% of 150 is 30. Three ways to calculate it, plus the mental-math trick you can use at restaurants and shops.

What is 25% of 80? (Answer + Easy Mental Math)

Published: May 11, 2026

25% of 80 is 20. Here's why dividing by 4 gets you the answer in one step, plus worked examples for discounts and tipping.

What is 10% of 1000? (And Why 10% Is the Easiest Percentage)

Published: May 10, 2026

10% of 1000 is 100. Move the decimal one place — that's it. Plus the mental-math foundation that lets you calculate any percentage fast.

Percentage Increase from 50 to 75 (Answer + Formula)

Published: May 9, 2026

Going from 50 to 75 is a 50% increase. Here's the formula, three worked examples, and how to avoid the most common percentage-increase mistake.

How to Calculate Percentage Decrease (Formula + Examples)

Published: May 8, 2026

Percentage decrease = ((Old − New) ÷ Old) × 100. Step-by-step examples for discounts, weight loss, stock drops, and revenue declines.

How to Calculate 30% Off $80 (Answer + 3 Methods)

Published: May 7, 2026

30% off $80 is $24 off, paying $56. Three ways to do the math in your head, plus when retailers stack discounts.

What is 50% Off $200? (Half Off Explained)

Published: May 6, 2026

50% off $200 means you save $100 and pay $100. Here's why half-off is the simplest discount math — plus when 'half off' is actually a mediocre deal.

Stacked Discounts Explained: Why 30% + 20% Off Isn't 50% Off

Published: May 5, 2026

Stacked discounts multiply, they don't add. Here's the formula and worked examples so you know what you're actually paying at checkout.

Tip on a $45 Bill (15%, 18%, 20%, 25%)

Published: May 4, 2026

Standard tip on a $45 bill: $6.75 at 15%, $8.10 at 18%, $9 at 20%, $11.25 at 25%. Mental-math shortcuts and split-the-bill amounts.

How Much is 20% Tip on $50? (Answer + Mental Math)

Published: May 3, 2026

20% tip on a $50 bill is $10, total $60. Here's the 'divide by 5' shortcut plus a reference table for nearby bill amounts.

How to Split a Restaurant Bill (Even, Uneven, with Tip and Tax)

Published: May 2, 2026

Five fair ways to split a restaurant bill — even split, by item, weighted, with proportional tip, and how apps like Splitwise handle the math.

Sales Tax on a $100 Purchase (US State-by-State)

Published: May 1, 2026

Sales tax on $100 ranges from $0 (Oregon, Delaware) to $10.25+ (parts of California, Tennessee). State rates and how to calculate yours.

Reverse Sales Tax Calculation (Get Pre-Tax Price from Total)

Published: April 30, 2026

Pre-tax price = Total ÷ (1 + tax rate). Work backwards from a receipt to find the original price before tax — formula, examples, and common use cases.

EMI on a $10,000 Personal Loan at 12% (3 / 5 / 7 Years)

Published: April 29, 2026

A $10,000 personal loan at 12% costs $332.14/mo over 3 years (total interest $1,957) or $222.44/mo over 5 years (total interest $3,347). Full math.

Monthly Mortgage Payment on $300,000 at 6.5% (15 vs 30 Years)

Published: April 28, 2026

A $300,000 mortgage at 6.5% costs $1,896/mo over 30 years (total interest $382,557) or $2,613/mo over 15 years (interest $170,420). Full math.

$500 Monthly SIP for 10 Years at 12% Return

Published: April 27, 2026

Investing $500/month for 10 years at 12% expected return grows to approximately $115,019. You invest $60,000; gains are $55,019. Full math.

Compound Interest on $10,000 at 8% for 20 Years

Published: April 26, 2026

$10,000 at 8% compound interest for 20 years grows to $46,610 with annual compounding, $49,268 monthly. Why time matters more than rate.

How to Calculate Percentage Increase and Decrease in Business: Complete Guide with Examples

Published: April 19, 2026

Learn how to calculate percentage increase and decrease for business growth, profit margins, and financial analysis. Step-by-step formulas with examples.

Mastering Percentage Increase and Decrease: A Complete Guide

Published: January 14, 2026

Learn how to calculate percentage increase and decrease with simple formulas and real-world examples. Perfect for business, finance, and students.

How to Calculate Percentages in Excel and Google Sheets

Published: January 14, 2026

Learn the best formulas to calculate percentages in Microsoft Excel and Google Sheets. Step-by-step guide for beginners and professionals.

How to Calculate Student Grade Percentages

Published: January 14, 2026

A simple guide for students and teachers on how to calculate grade percentages, weighted averages, and GPA.

Percentage Difference vs. Percentage Change: When to Use Which?

Published: January 12, 2026

What is the difference between percentage difference and percentage change? Learn when to use each formula with clear examples.

How to Calculate Sales Tax and Discounts Manually

Published: January 10, 2026

Learn how to calculate sales tax and discounts manually with simple percentage formulas and worked examples for shopping and small business.

How to Calculate Percentage of Marks for Exams

Published: January 8, 2026

Learn how to calculate percentage of marks for 10th, 12th, and University exams using our simple formula and step-by-step guide.