Paycheck basics
Gross pay vs. net pay: where the difference comes from
Understand the difference between gross pay, taxable wages, deductions, taxes, and net pay with a worked paycheck example.
Read guideResources
Understand the math behind the calculators
Use PayCalc's resource library to understand the rules, formulas, assumptions, and tradeoffs behind paycheck, mortgage, and investment estimates.
Practical explanations behind the numbers
These articles expand on the assumptions behind PayCalc's tools. They use worked examples and link to primary government sources where rules or regulatory concepts are involved.
Federal withholding
How Form W-4 changes federal withholding
A practical explanation of Form W-4 Steps 2, 3 and 4 and how they flow into federal paycheck withholding.
Read guideFICA taxes
Social Security and Medicare are separate paycheck taxes
Learn how Social Security, Medicare, the annual Social Security wage base, and Additional Medicare withholding affect a paycheck.
Read guideSupplemental wages
Why bonus withholding can look different from regular withholding
Understand the federal rules for bonuses and other supplemental wages, including the 22% optional flat method and the $1 million threshold.
Read guidePaycheck deductions
Not every pre-tax deduction reduces the same taxes
Learn why traditional 401(k) and Section 125 deductions can affect federal taxable wages, Social Security, Medicare, and net pay differently.
Read guideMortgage mechanics
How a fixed-rate mortgage amortizes
Understand fixed-rate mortgage amortization, principal and interest, why early payments are interest-heavy, and how payoff develops over time.
Read guideMortgage payoff
Why extra principal payments can save interest
Learn how additional principal payments can shorten a fixed-rate mortgage and reduce interest, with a worked example and important caveats.
Read guideMortgage insurance
PMI can change the monthly cost without reducing your loan balance
Learn what private mortgage insurance is, how it affects monthly cost, and why a simple mortgage calculator should not assume PMI lasts forever.
Read guideMortgage comparison
15-year vs. 30-year mortgage: what actually changes
Compare 15-year and 30-year fixed mortgages by payment, total interest, flexibility, and the effect of rate differences.
Read guideInvestment math
Compounding frequency changes the meaning of a return input
Understand compound growth, compounding intervals, effective returns, and why a percentage per month is not the same as the same percentage per year.
Read guideInvestment planning
A return assumption is a scenario input, not a forecast
Learn how to use return assumptions responsibly in investment projections without treating historical averages as guaranteed future results.
Read guideRental property
Rental yield and ROI answer different questions
Understand gross rental yield, net rental yield, and why they are not the same as a complete real-estate return on investment calculation.
Read guideScenario planning
Use an investment calculator to compare scenarios, not predict one future
A practical framework for comparing investment projections using multiple rates, durations, and compounding assumptions instead of a single forecast.
Read guideHow this library is maintained
PayCalc prioritizes primary sources such as the IRS, Consumer Financial Protection Bureau, and Investor.gov. Tax-year-sensitive material is reviewed when calculator rules are updated. General financial examples are labeled as examples rather than recommendations.
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