Every FigureNerd calculator goes through extensive industry-specific investigative research. We name our sources and document our formulas. No black-box math.
FigureNerd calculators start with a question a real person is trying to answer: "How much HVAC do I need for a Minnesota winter?" or "Does switching to an S-corp actually save me money?" We do not start with a formula from a textbook and work outward. We start with the real-world problem and work backward to find the right formula.
Every calculator follows a three-layer methodology. It is the same process whether we are building an HVAC load sizing tool or a retirement runway stress-test. The layers are not optional. A calculator cannot ship until all three are complete.
We read the top three competitor tools for each topic. We document what they get right and where they fall short, including regional adjustments they miss, edge cases they ignore, and explanations that assume too much. Calculator.net is always one of the three because they are the volume leader in the calculator space.
We identify the authoritative data source for each topic: ACCA Manual J for HVAC sizing, IRS publications for tax, NEEP for heat pump performance, Fannie Mae guidelines for mortgage, RSMeans for construction. We read the source documents, not the summaries.
The calculator and its documentation file are built at the same time, not after. Every formula gets a co-located documentation file with eight required sections: experts referenced, reference tools benchmarked, formula derivation, regional factors, test cases, disclaimer, sources, and update log.
Every calculator names its primary source on the tool page. We link to the actual document, not just the agency homepage. Here is the full list of primary sources by topic:
When tax rates change (IRS updates brackets and limits each year in October and November), we update the affected calculators before January 1. When EPA regulations change refrigerant rules, we update the HVAC calculators. When FHFA publishes new conforming loan limits, we update the mortgage tools.
The update process follows the same three-layer methodology as the initial build. We do not just change a number. We verify the new rate against the primary source, update the formula documentation, and confirm the change does not break any of the locked test cases.
Each topic area has its own primary authority and formula approach. Here is how we build within each one:
Load sizing follows ACCA Manual J with IECC climate zone multipliers. Heat pump performance uses NEEP ccASHP published category averages at 47F, 17F, 0F, and -13F. Refrigerant comparison uses EPA AIM Act GWP figures and phase-down timeline.
Source: ACCA Manual J, 8th Ed.Self-employment tax uses the 92.35% net earnings multiplier from IRS Publication 334. Quarterly estimates use the safe harbor rules from IRS Publication 505. S-corp reasonable compensation benchmarks come from BLS Occupational Employment Statistics.
Source: IRS Pub 334, 505, 5351031 exchange failure cost uses the depreciation recapture rate (25%), LTCG rates, and NIIT (3.8%) from IRC sections 1245, 1250, 1411, and 1031. Fannie Mae and FHFA set the conforming loan limits used in mortgage tools.
Source: IRC 1031, IRS Pub 544Heat pump payback uses DOE climate zone COP adjustments, ENERGY STAR product specifications, and the IRS 25C credit limits that applied through December 31, 2025 (the credit is now expired and off by default in the calculator). EV charging cost uses EIA state electricity price data and manufacturer-published charge efficiency ratings.
Source: DOE, ENERGY STAR, IRS 25CDrywall quantity uses the RSMeans industry-standard formula (square footage plus waste factor plus door and window deductions).
Source: RSMeans Cost DataRetirement withdrawal uses Social Security Administration benefit rules, state-by-state Social Security taxability rules (approximately 9 to 10 states tax SS benefits as of 2026), and sequence-of-returns modeling. Longevity scenarios run to age 100.
Source: SSA, IRS Pub 915All primary sources used across FigureNerd calculators, with direct links to the authoritative documents:
Have a question about a specific calculator's methodology? The documentation file for each calculator is available by request. Contact us via the feedback link on any calculator page.