The four problem groups in this category
The ten calculators here cluster around four distinct financial-math problems. Loan amortization (mortgage, loan, auto loan) all share the same underlying formula — periodic payment of a fixed-interest amortizing loan — and differ mainly in the typical rate ranges and the supporting context (PMI for mortgages, credit-tier APRs for auto loans, etc.). Time-value-of-money calculators (compound interest, ROI) translate principal-and-rate inputs into future or annualized values; the formulas are simple, but the misconceptions around them are the deepest. Personal compensation (salary, tip) deals with conversion between gross and net amounts under specific tax and convention rules. Pricing (discount, margin/markup) handles the relationship between cost, price, and the real money that ends up in someone's pocket.
Rent-vs-buy sits across all four — it borrows amortization for the mortgage leg, time-value-of-money for the opportunity cost on the down payment, and pricing judgment for transaction costs. That's why it has its own dedicated guide.
All ten finance calculators
Mortgage Calculator
Monthly principal + interest using the standard amortization formula. Includes PMI and tax/insurance context.
Loan Calculator
Personal/general loan payments, total interest paid, and amortization. APR vs interest rate explained.
Auto Loan Calculator
Car loan payments with credit-tier APR ranges, down payment effects, and the upside-down loan trap.
Compound Interest Calculator
A = P(1+r/n)^(nt). Rule of 72, continuous compounding, and the math behind early investing.
ROI Calculator
Return on Investment with simple, annualized, and IRR perspectives. Real vs nominal returns.
Salary Calculator
Hourly to annual conversions, FICA, federal brackets 2024-25. Gross-to-net at a glance.
Tip Calculator
Pre-tax vs post-tax tipping, US service-industry conventions, and international tipping norms.
Discount Calculator
Original price × discount rate. The fake-discount problem (FTC 16 CFR 233) and anchoring psychology.
Margin & Markup Calculator
Margin = Profit/Revenue, Markup = Profit/Cost. Industry typical margins and the common confusion explained.
Rent vs Buy Calculator
Five-year breakeven analysis with maintenance, taxes, opportunity cost on the down payment.
Recommended reading
Understanding Compound Interest: How Your Money Actually Grows
The formula, frequency, the Rule of 72, and why starting early matters more than the rate itself.
Rent vs Buy: The Real Math Behind Homeownership
Why "rent is throwing money away" is mostly wrong. The 5-year rule and regional differences.
How to Budget: The 50/30/20 Rule (and When It Doesn't Work)
Elizabeth Warren's framework, where it works, and where it breaks down (high-cost cities, high debt).
Editorial standards for this category
Finance is YMYL (Your Money or Your Life) content under Google's quality guidelines, and we treat it accordingly. Every formula is implemented from the standard published equation, every rate or threshold cited is sourced from a current primary document (CFPB rulings, IRS publications, Federal Reserve FRED data, Freddie Mac PMMS for mortgage rates, FHFA for conforming loan limits), and every limitation is made explicit. These tools do not constitute financial advice; they implement the math correctly so you can have an informed conversation with a fiduciary, lender, or accountant.
CalcNow Finance Team
A small team of contributors who research, build, and review the finance and business calculators on CalcNow. We are not licensed financial advisors and CalcNow does not provide individualized financial advice.
Coverage: Mortgages, personal & auto loans, compound interest, ROI, salary structures, business margins, rent-vs-buy analysis
Editorial standard: Every finance article is cross-checked against primary public sources — CFPB, IRS, Federal Reserve (FRED), FHFA, SEC investor.gov, and peer-reviewed finance journals — before publication. We update articles when the underlying rates, brackets, or rules change.