Sources and how we write
CalculateItEasy publishes calculators and explainers for everyday US money decisions: rent, mortgages, paychecks, and savings. The math on a calculator is ours. The rules of thumb we explain come from somewhere, and this page says where.
We read public guides, housing reports, and a small number of well-known personal-finance books. We then write the explanation ourselves, with a worked example and the limit of the rule. We do not copy chapters, paste report tables in full, or present an estimate as a decision a lender or a tax agency has made for you.
When a figure can go stale — a debt-to-income cap, a tax form, a survey year — the article names the document and the date we checked it. If you find a number that has moved, write to help@calculateiteasy.com.
Books
All Your Worth: The Ultimate Lifetime Money Plan
Elizabeth Warren and Amelia Warren Tyagi, Free Press, 2005. This is the book that set down the Balanced Money Formula: about 50% of take-home pay for must-haves, 30% for wants, and 20% for savings. Our 50/30/20 guide describes that split and works an example. It does not reproduce the book.
Related guideThe Two-Income Trap
Elizabeth Warren and Amelia Warren Tyagi, Basic Books, 2003. The earlier book, based on bankruptcy research, about why two earners can still have no cushion. We mention it only as background for why All Your Worth was written.
Related guide
Official and research sources
- HUD USER, on the 30% housing measure
Brooke Amendment (1969) 25% public-housing rent cap, the 1981 increase to 30%, and HUD’s cost-burden definition.
- Harvard Joint Center for Housing Studies, America’s Rental Housing 2026
2024 counts: 22.7 million cost-burdened renter households (49%), including 12.1 million severely burdened (26%).
- Fannie Mae Selling Guide, B3-6-02, Debt-to-Income Ratios
Manual DTI maximum of 36%, up to 45% with Eligibility Matrix requirements; Desktop Underwriter maximum of 50%.
- Fannie Mae Selling Guide, B3-6-03, Monthly Housing Expense
What goes into PITIA: principal, interest, taxes, insurance, mortgage insurance, and association dues.
- Federal Reserve, Economic Well-Being of U.S. Households in 2025
Savings findings from the October 2025 survey, published May 2026, including the $400 expense and three-month cushion questions.
- US Department of Labor, overtime
Fair Labor Standards Act overtime is generally owed after 40 hours in a workweek for nonexempt employees.
- IRS Publication 15-T
How employers withhold federal income tax from wages using Form W-4.
- Social Security Administration, contribution and benefit base
The annual wage cap for the 6.2% employee Social Security tax. Medicare employee tax remains 1.45% with no wage cap.
What the calculators are
A calculator applies the inputs you type to a formula shown on that page. It does not pull your credit report, your lease, or your tax return. Results are estimates. Read the disclaimer before you treat a result as a budget you must hit. Who operates the site is on the about page.