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METHODOLOGY & EDITORIAL STANDARDS

Every calculator here shows its work. This is how that work gets done.

This page is the long version of the four-step method on the About page: how every calculator on CalcWise is built, from the first IRS publication I open to the date stamp on the finished page, and the editorial standards that govern what goes on each one. The short version is that a calculator that shows its work is more useful than a black box, even when the numbers are a year old, because you can see the method and adjust it yourself. The rest of this page is the long version.

THE METHOD

The method, step by step

Every calculator here follows the same four steps, in this order. Skip a step and the whole point of the site is gone.

  1. Step 1: Start from the source

    Before any formula gets written, I go to the actual source. For tax calculators that means the IRS publication, the form and its current-year instructions, the Internal Revenue Code section, or the Revenue Procedure that sets the year's inflation-adjusted figures. For non-tax topics it means the federal agency that actually governs the rule: the Department of Labor for FLSA overtime, the SBA for loan programs, the Social Security Administration for self-employment tax, the Federal Reserve or CFPB for lending rules.

    I do not start from a blog summary or a tax software company's guidance page. Those are useful for pointing me toward the right primary source, and I will read them to find it, but the citation on the finished page points at the .gov page, not the summary. The reason is simple: summaries get the numbers wrong, get them right but out of context, are themselves working off a stale summary, or drop a condition that changes the answer. The IRS publication is the thing the summary is trying to summarize. I go there.

    The MACRS depreciation calculator pulls its percentages from the tables in Appendix A of IRS Publication 946. MACRS stands for Modified Accelerated Cost Recovery System, the depreciation method most business assets use. I opened Pub 946, read the tables, and built the engine to reproduce them. The hard part is the convention, half-year or mid-quarter or mid-month, which decides how much depreciation you get in the first and last year. Get the convention wrong and every year of the schedule shifts. That is why step 2 exists, and why the test suite spends so much time on the boundaries between conventions.

  2. Step 2: Check the math

    A formula is not done when it is written. It is done when its output matches a worked example in the source, dollar for dollar, for every distinct calculation path the calculator handles.

    For each calculator I work the math by hand first, using a worked example straight out of the IRS publication or form instructions. Then I code it. Then I write test cases that encode those same worked examples and run them against the code. If the code's output does not match the source's number, the code is wrong, and I fix it before the calculator goes anywhere near the site.

    The test cases stay in the codebase and run every time the engine changes. That matters because a depreciation schedule has a dozen moving parts (basis, business-use percentage, recovery period, convention, Section 179 election, bonus depreciation, regular MACRS), and a change to one of them can break another in a way that is hard to spot. The tests catch that.

    The MACRS test suite has cases pulled from Pub 946's own worked examples, plus edge cases at the boundaries: 50% business use, the 40% mid-quarter threshold that flips the convention, a basis of zero, inputs that should trigger a warning. Each dollar-amount case has an expected result that came from the source, not from my arithmetic. If a future change to the engine breaks one of those cases, the test fails and the calculator does not ship until I fix it.

  3. Step 3: Show the work

    This is the whole point of the site. Every calculator puts the formula, the assumptions, and the sources on the page next to the result, where you can read them.

    Specifically, each calculator page has:

    • The formula, in plain English and in the order it runs. For the MACRS calculator that is basis, then Section 179, then bonus depreciation, then regular MACRS, in that order, because that is the order the IRS specifies.
    • The assumptions the calculator is making, written out as a list. Not buried in code comments. On the page.
    • The sources, with links to the actual IRS publication or federal page each figure came from.
    • The limitations, surfaced as warnings on the page. If the calculator does not model your situation, it tells you, rather than handing you a number that does not apply.

    The reason this matters: a number you cannot check is a number you have to trust. A number you can check is a number you can verify, adjust, or reject on your own terms. If the Section 179 limit on the page is last year's figure and you know this year's is higher, you can swap in the current number and re-run the math. You cannot do that with a black box, because you do not know which number is which.

  4. Step 4: Keep it current

    Tax rules change. Inflation-adjusted limits change every year. Sometimes a rule changes mid-year, like the bonus depreciation shift in 2025. A calculator that does not track that is wrong, and a calculator that is wrong but does not tell you it is wrong is worse than no calculator at all.

    Every calculator page carries two dates: the tax year the figures are drawn from, and the date I last reviewed the page. When a figure changes, I update the calculator, update the date, and note what changed.

    For inflation-adjusted figures (Section 179 limits, retirement contribution limits, the standard deduction, earned income credit tables), the source is the annual Revenue Procedure the IRS publishes, usually in the fall for the following tax year. I confirm each figure against that Rev. Proc. before the calculator goes live for that year. If the Rev. Proc. is not out yet and I am running a placeholder, the calculator says so, in a warning on the page, with the year and the reason. I would rather flag a placeholder than ship a number I have not confirmed and pretend it is official.

SOURCES

Sources, in strict order

Not all sources are equal. A number from the Internal Revenue Code is the law. A number from a tax software company's help page is someone's summary of the law. I cite in a strict order, and the order matters.

The hierarchy, highest authority first:

  1. IRS primary sources. IRS publications (Pub. 946 for depreciation, Pub. 535 for business expenses, Pub. 560 for retirement plans), the forms and their current-year instructions, Revenue Procedures for inflation adjustments, Revenue Rulings and Notices for specific guidance, and the Internal Revenue Code and Treasury Regulations themselves. These are the law and the IRS's own explanation of the law.
  2. Other federal sources. The Department of Labor for FLSA and wage-and-hour rules, the SBA for loan programs, the Social Security Administration for self-employment tax, CMS, the Federal Reserve, the CFPB. The official .gov page, not a third-party rewrite.
  3. Authoritative industry and academic sources. FASB, AICPA, NAR, major university extension pages. I use these only when no IRS or federal source applies, for example for a bookkeeping definition that the IRS does not define.
  4. Reputable secondary sources. Major tax software publishers' guidance pages, Big Four tax guides. I use these to locate the primary source, never as the final citation. If a Big Four guide says the Section 179 limit is a given number, I go find the Rev. Proc. that says so and cite that. The guide was a pointer, not the source.

Two rules that do not bend. I never cite a source I have not opened. And I never round a source's number and present the rounded value as the official figure. The full precision goes in the engine; rounding happens only for display. If a table in the source gives a percentage to three decimal places, the engine stores all three, not a rounded two.

EDITORIAL STANDARDS

What goes on every page

These are the editorial standards every calculator page meets. They are the concrete version of the four-step method.

  • Every result links back to the rule or form it came from. The sources sit on the page, with links, not in a footnote you have to hunt for.
  • The formula and the assumptions are on the page, not hidden. You can read the math the calculator ran, in order, and the assumptions it made along the way.
  • Calculators are dated. Each page shows the tax year its figures come from and the date I last reviewed it. When the numbers change, the page changes, and the date changes with them.
  • If a calculator does not model your situation, it tells you. Every limitation is a warning on the page, not a silent assumption in the code. (More on this in the next section.)

And one commitment that ties it together: if you spot a mistake, tell me, and I will fix it and note what changed. The corrections section below has the details.

THE BOUNDARY

What calculators won't model

Every calculator has a scope, and the scope is smaller than real life. Here is the boundary, stated on the page rather than buried in the code.

Here is what the v1 calculators do not model, and what happens instead:

  • State rules. The calculators are federal only. State depreciation rules, state Section 179 conformity, state bonus depreciation decoupling, state income tax rates: all out of scope. Many states decouple from bonus depreciation and Section 179 entirely. The calculator surfaces this as a warning on the page, because a federal deduction and a state deduction are not the same number. Modeling state rules without a sourced state-by-state table would mean inventing figures, and I will not do that.
  • Income limits and phase-outs, where noted. Some deductions and contributions phase out above an income threshold. Where the calculator does not model the phase-out, it says so.
  • Auto caps. Listed property and passenger vehicles have their own depreciation caps under Section 280F. Where a calculator does not model the caps, it warns you.
  • Same-year disposal and short tax years. These edge cases change the math in ways the general calculators do not handle. The calculator tells you it does not handle them rather than returning a number that looks right and is not.

The principle: a calculator that tells you what it cannot do is more trustworthy than one that pretends it can do everything. A warning that says "this estimate does not include your state's rules" is more useful than a number that ignored them anyway.

KEEPING IT CURRENT

When the rules change

Tax figures do not hold still. Inflation-adjusted limits move every year, and legislation rewrites rules mid-year sometimes. A calculator that was correct in January can be wrong by July, and the only honest response is to track it and tell you.

How figures get verified. For inflation-adjusted figures (Section 179 limits, retirement contribution limits, the standard deduction, earned income credit tables), I confirm each one against the year's Revenue Procedure before the calculator goes live for that year. The Rev. Proc. is the IRS document that sets inflation-adjusted numbers for the coming tax year, usually published in the fall. Until it is out and I have confirmed the figure, the calculator carries a warning that names the year and says the figure is not yet confirmed.

The mid-year problem. In 2025, the One Big Beautiful Bill Act changed bonus depreciation mid-year. The rate was 40% for property placed in service before January 19, 2025, and 100% for property placed in service on or after that date. A calculator that applies one rate to all of 2025 is wrong for half the year. The MACRS calculator handles the date boundary because the rule has a date boundary. A calculator that ignores a mid-year change is not a calculator with a small caveat. It is a wrong calculator.

What happens when a source moves. IRS pages get reorganized. A URL that worked last year 404s this year. When that happens, I trace the figure to the current canonical URL and update the citation. A stale link is a small problem. A stale number is a big one. I fix both, but the number is the one that matters.

The annual cycle. Every fall I re-verify the inflation-adjusted figures against the new Rev. Proc., update the calculators, update the tax-year stamp and the last-reviewed date, and note what changed. I re-check figures that are not inflation-adjusted when the underlying rule changes, not on a fixed schedule.

CORRECTIONS

Corrections

If you spot a wrong number, a broken link, a stale figure, or a formula that does not match the source, tell me. Email aaron@calcwise.org. That is the most useful email this site can get. For what to include when you report a wrong number, see the Contact page.

Here is what happens when a correction comes in and I confirm it is right: I fix the error, update the last-reviewed date on the page, and note what changed. The note lives on the page or in a changelog, so the correction is visible, not hidden.

Honest about the turnaround: I am one person. I read everything that comes in. I cannot promise a fast reply, but I do read it, and confirmed errors get fixed. If the error is load-bearing, meaning it would change a real filing or a real decision, I treat it as urgent and fix it before anything else.

One thing I will not do is delete a mistake and pretend it did not happen. If a figure was wrong and people may have used it, the correction note says what it was, what it is now, and when it changed.

THE HONEST LIMIT

The review gap, stated plainly

I built every calculator, and I review every calculator. There is no second person checking the math, no independent CPA or enrolled agent signing off before a page goes live. That is a real weakness, and I am not going to dress it up.

It is also not nothing. The same person who read Pub 946 is the person who wrote the formula, coded it, wrote the tests, and re-checked the figures. When I review, I am not handing unfamiliar work to a stranger. I am checking my own math, which means I know where the hard parts are and where I am most likely to have gone wrong. That is weaker than an independent review and stronger than no review at all.

The plan to close the gap: add an independent CPA or enrolled agent as a named reviewer, with their name and credential on the pages they check. That is a specific step I am working toward, not a vague aspiration. When it happens, this page will say so, and the reviewer's name will appear on the calculators they signed off on.

Until then, the honest framing is this: every figure here was researched and checked by one person who is not a CPA, EA, attorney, or CFP. Use the calculators to plan and to understand the math. For a number that real money or a real filing depends on, take it to a qualified professional and confirm it.

NOT ADVICE

Not advice

Last reviewed July 6, 2026.