Methodology
How we calculate
The formulas, official figures and assumptions behind every CalcDime calculator, and how we keep them current. Last reviewed November 2026.
Official figures in use
Tax and contribution figures come directly from IRS and Social Security Administration publications, not from secondary sources. The calculators currently use the values for the 2026 tax year:
| Figure | 2026 value | Source |
|---|---|---|
| Federal income tax brackets | 10% to 37%, by filing status | IRS Rev. Proc. 2025-32 |
| Standard deduction | $16,100 single · $32,200 joint · $24,150 head of household | IRS Rev. Proc. 2025-32 |
| Social Security wage base | $184,500 (6.2% employee rate) | SSA |
| Medicare tax | 1.45%, plus 0.9% above $200,000 ($250,000 joint) | IRS Topic 560 |
| 401(k) employee limit | $24,500 · $32,500 at 50+ · $35,750 at 60–63 | IRS Notice 2025-67 |
| IRA contribution limit | $7,500 · $8,600 at 50+ | IRS Notice 2025-67 |
| Roth IRA income phase-out | $153,000–$168,000 single · $242,000–$252,000 joint | IRS Notice 2025-67 |
When the IRS and SSA publish figures for a new year — usually in October and November — we move to them at the start of that tax year, since paychecks and contribution limits follow the calendar year.
Calculation conventions
Loans
Mortgages, auto loans and personal loans use the standard fixed-payment amortization formula with monthly interest at one-twelfth of the annual rate. Schedules are computed month by month, and the last payment is only what remains, so totals are exact rather than payment × months. Personal loan APR is solved numerically so that the payment repays the amount actually received after fees.
Savings and investments
Deposits are made monthly at the end of each month. Annual returns are converted to an equivalent monthly rate, so a 7% return means 7% over a full year. Projections are nominal unless a page says “today’s dollars”, in which case the result is divided by (1 + inflation)years.
Taxes
The paycheck calculator computes the annual tax for the full salary and spreads it evenly over pay periods. Federal tax applies the brackets marginally after the standard deduction. FICA is applied to wages after cafeteria-plan health premiums but before 401(k) contributions, matching how payroll systems treat them.
Dates and rounding
Payoff dates count forward from the current month and assume the first payment is due next month. Figures are calculated at full precision and rounded to the nearest dollar only for display.
What the calculators do not do
- They do not model variable rates, missed payments, or changes to the law after the review date.
- They do not include tax credits, itemized deductions, local taxes or state tax brackets.
- Investment returns are assumptions, not forecasts. Real returns vary from year to year and can be negative.
Every calculator page lists its own assumptions and what it leaves out.
Privacy of your inputs
All calculations run in your browser. The numbers you type are not sent to our servers or stored. See the privacy policy for details on cookies and advertising.
Corrections
If a result looks wrong, contact us with the calculator name and the inputs you used. We check every report and update the page and its review date when a fix is needed.