Finance & Money
Understand financial percentages including ROI, interest rates, profit margins, and investment calculations with expert insights.
What You Will Learn
Financial percentages — ROI, interest, margins, tax — decide whether money grows or leaks. A 1% fee difference compounded over 20 years can cost tens of thousands, so precision matters.
Use ROI = ((Gain − Cost) ÷ Cost) × 100 for investments, and compound growth A = P(1 + r/n)^(nt) for savings. Our finance calculators expose every input so you can audit the math.
Below are the highest-impact tools: discount and tax for spending, compound interest and mortgage for wealth building. Each includes US-specific examples.
Start With These Tools
Discount + Sales Tax — True Cost
Combine discounts and tax to see what you actually pay at checkout.
Calculate Your DiscountCompound Interest — Growth Engine
Project savings growth with contributions, rate, and compounding frequency.
Project Investment GrowthMortgage — Monthly Payment
Estimate principal + interest before you talk to a lender.
Estimate Mortgage PaymentIn-Depth Articles
Compound Interest Explained: Formula, Examples, Rule of 72
Compound interest explained simply: the A = P(1+r/n)^nt formula, 3 verified examples, the Rule of 72, and the fee mistake that costs thousands.
10 min read
Read ArticleCommon Questions
What is a good ROI percentage?
Context-dependent: 7–10% annualized is a common long-term stock-market benchmark before inflation; compare against risk and fees.
How do I calculate profit margin vs markup?
Margin = (Profit ÷ Revenue) × 100. Markup = (Profit ÷ Cost) × 100. A $20 profit on $80 cost is 25% margin but 33.3% markup.
Should I use APR or APY?
APR ignores compounding, APY includes it. For savings, compare APY; for loans, compare APR plus fees.
Last updated: · Reviewed by PercentLab Editorial Team
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