Methodology and Data Sources
This page distinguishes the sources for factual rules from the assumptions used in examples and calculators. A source link, a reproducible calculation, and an editorial review answer different questions. If a claim here disagrees with its source, please tell us which page and claim need checking.
The rule sources: where the rules themselves come from
These are the reference authorities for the topics below. A link to an agency is a starting point; the specific publication, effective year, and scope still need to match the claim:
| Topic | Primary authority |
|---|---|
| Federal taxes, retirement account rules and limits | Internal Revenue Service |
| Consumer credit, debt collection, mortgages, banking practices | Consumer Financial Protection Bureau |
| Investing basics, fund structures, fraud | SEC and Investor.gov, FINRA |
| Deposit insurance | FDIC |
| Social Security, Medicare premiums | SSA, Medicare.gov |
| Workplace benefits, wage and hour rules | Department of Labor |
The running reference list lives on the Sources page, and individual guides cite the specific pages they rely on in a “Sources and further reading” section.
Static references and illustrative numbers
The current site does not provide live market, inflation, mortgage-rate, or currency feeds. Published guides and tax assumptions are static references. A link to an official source does not automatically update the text or a calculator when that source changes.
Balances, interest rates, returns, and household amounts in worked examples are illustrative inputs unless a page explicitly attributes them to a dated observation. They are not market quotes, measured household outcomes, or forecasts. Their purpose is to show what changes when an assumption changes.
A comparison table organizes stated differences. A checklist identifies questions or documents to gather. Neither is a numerical model simply because it is presented as a table. Factual rows need supporting references; editorial suggestions need to be identified as suggestions. The page should explain which kind of work it contains.
How we handle numbers that go stale
These are the standards for maintaining time-sensitive figures:
- Prefer the mechanism over the number. Explaining how a threshold works stays true for years. Quoting the threshold itself goes out of date every January. Where the mechanism is enough, we explain the mechanism.
- State the applicable year or date. A tax-year label identifies the rules used in a calculation. A page’s update date is not a substitute for that label and does not prove that every rule was rechecked.
- Link the live source. For figures that change annually, we point to the official page carrying the current number rather than asking you to trust a static copy of it.
- Make uncertainty explicit. If a current figure cannot be verified, omit it or flag the limitation and direct the reader to the authority responsible for it.
How the calculators and decision tools work
The 16 tools on this site run entirely in your browser. No financial numbers you type are sent to The Penny Plan, stored by the tools, or attached to an account: the arithmetic happens on your device.
Each calculator page shows its formula or calculation steps and assumptions. Mortgage and loan tools calculate payments and balances from the supplied principal, rate, and term. Savings and retirement tools use the supplied contributions, time, and assumed return; they do not retrieve a current return or predict a future one.
The Paycheck Calculator uses 2026 single-filer federal income-tax brackets and the standard deduction. It separately models the Social Security wage cap, regular Medicare, and Additional Medicare above the stated threshold. Traditional 401(k) deferrals reduce income-tax wages but not Social Security or Medicare wages; the separate benefits field is limited to qualifying deductions exempt from both. An optional state tax input is a flat estimate. Annual estimates are spread across pay periods, so the result is not W-4 withholding or an exact paycheck.
The Salary-to-Hourly Calculator converts pay using the hours, weeks, paid leave, and overtime inputs. Its optional after-deduction column uses one flat percentage supplied by the reader. It does not calculate federal tax brackets, Social Security, or Medicare. These two tools answer different questions and their net-pay estimates are not interchangeable.
The calculators are educational estimates, not quotes, offers, or professional tax or financial advice. Real terms depend on your lender, your employer, your state, and your full situation.
Money Priority Planner method
The Money Priority Planner combines four calculations that are usually separated:
- Monthly cash-flow margin equals take-home income minus essential expenses and required debt minimums.
- Emergency runway equals liquid emergency savings divided by one month of essential expenses and required debt minimums.
- Illustrative annual debt cost equals the current balance multiplied by APR. This is a simple snapshot, not a payoff forecast, because the balance should fall as payments are made.
- Possible unclaimed employer match equals the plan’s maximum match under the inputs minus the match captured at the current contribution rate. The planner cannot read an employer’s plan document, vesting schedule, eligibility rules, or payroll treatment, so the result is explicitly labelled an estimate to verify.
The planner uses a three-month emergency reserve as its base comparison and adds one month for each user-selected risk factor: variable income, a one-earner household, and dependents, capped at six months. That is a transparent risk illustration built around the common three-to-six-month range, not a claim that the resulting target is correct for every household.
The 30-day map is a decision aid, not an optimization engine. It first flags a negative monthly margin, then a gap below one month of essential obligations, then a possible unclaimed employer match, and finally the trade-off between a fuller reserve and extra debt payments. It explains which condition triggered the stage so the reader can disagree with the sequence and still use the calculations.
Validation and limits
The calculator test suite includes known scenarios and edge cases: zero-interest loans, payments that do not cover monthly interest, empty optional fields, negative cash flow, fully funded reserves, retirement contributions above the employer-match cap, and paycheck tax thresholds. These tests check the implemented arithmetic and selected behaviors. They do not establish that a rule remains current, validate a reader’s inputs, or constitute professional review. Each tool’s assumptions and omissions remain part of the result.
Editorial standards
How pages are researched, reviewed, and corrected is documented separately in our Editorial Policy, including how AI tooling is used and where human responsibility sits. The Disclaimer is the controlling statement of what this site is and is not.