Our Methodology
How we verify every calculation for accuracy
Why methodology matters
Financial calculators influence real decisions — mortgage commitments, retirement planning, tax estimates. An error of even a few dollars per month compounds into thousands over a loan term. At accurate.software, we treat calculation accuracy as a non-negotiable requirement, not a nice-to-have feature.
Our verification process
- Formula sourcing. Every calculation uses standardized formulas from authoritative references: IRS publications, the Consumer Financial Protection Bureau (CFPB), Bureau of Labor Statistics, Bankrate, and Investopedia. We cite the specific source for each calculator below.
- Integer-cent arithmetic. We never use floating-point math for currency. All monetary calculations use integer cents internally, eliminating rounding drift that plagues most online calculators. Final values are precise to exactly two decimal places.
- Automated test suites. Every calculator function has comprehensive unit tests verified against known-good results from trusted sources. Tests cover correct outputs, edge cases (zero, negative, very large values), boundary conditions, and precision requirements.
- Amortization integrity checks. For loan-based calculators, we verify that the sum of all scheduled payments equals the total payment amount and that the final balance is exactly $0.00.
- Cross-source validation. We verify outputs against at least two independent sources (e.g., Bankrate calculator results and manual formula computation) before shipping any calculator.
Privacy by design
All calculations run entirely in your browser. Your financial data — income, loan amounts, savings balances — never leaves your device. There are no server round-trips and no accounts. We use cookieless, privacy-first analytics to understand usage patterns — but your financial inputs stay on your device. This also means calculations are instant with zero network latency.
Transparent formulas
Every calculator page displays the exact mathematical formula used, with full variable definitions. We believe you should be able to verify any result by hand. If our answer differs from your manual calculation, something is wrong — and we want to know about it.
Calculator-by-calculator reference
Mortgage Calculator
- Formula
- M = P [ i(1+i)^n ] / [ (1+i)^n – 1 ]
- Reference Sources
- Bankrate mortgage calculator
- Consumer Financial Protection Bureau (CFPB) amortization guidelines
- Precision Guarantee
- Monthly payment to 2 decimal places; amortization schedule sums to exact total with $0.00 final balance
- Edge Cases Tested
- Zero interest (principal ÷ months), 100% down payment, 1-month term
Compound Interest Calculator
- Formula
- A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) – 1) / (r/n)]
- Reference Sources
- Investopedia compound interest formula
- SEC.gov compound interest examples
- Precision Guarantee
- Future value to 2 decimal places; growth data per compounding period
- Edge Cases Tested
- Zero rate, zero contribution, daily vs annual compounding
Loan EMI Calculator
- Formula
- EMI = P × r × (1+r)^n / ((1+r)^n – 1)
- Reference Sources
- Bankrate loan calculator
- Reserve Bank of India EMI formula reference
- Precision Guarantee
- EMI to 2 decimal places; total interest and total payment verified against amortization sum
- Edge Cases Tested
- Zero interest, single-month tenure, very large principal
Retirement Savings Calculator
- Formula
- FV = PV(1+r)^n + PMT × [((1+r)^n – 1) / r]
- Reference Sources
- Investopedia retirement calculator methodology
- Fidelity retirement planning guidelines
- Precision Guarantee
- Projected savings to 2 decimal places; inflation-adjusted values computed separately
- Edge Cases Tested
- Zero return rate, zero contribution, retirement age equals current age
ROI Calculator
- Formula
- ROI = (Gain – Cost) / Cost × 100; Annualized = ((1 + ROI)^(1/years) – 1) × 100
- Reference Sources
- Investopedia ROI formula
- CFA Institute return calculation standards
- Precision Guarantee
- ROI percentage to 2 decimal places; annualized ROI to 4 decimal places
- Edge Cases Tested
- Zero investment period, negative returns, zero cost basis
Tax Calculator
- Formula
- Progressive bracket calculation: each income slice taxed at its marginal rate
- Reference Sources
- IRS Revenue Procedure (current tax year brackets)
- IRS Publication 17 standard deduction amounts
- Precision Guarantee
- Tax amounts to 2 decimal places; effective and marginal rates to 2 decimal places
- Edge Cases Tested
- Zero income, income below standard deduction, all filing statuses
Salary Calculator
- Formula
- Conversions between annual, monthly, biweekly, weekly, daily, and hourly using standard work-year assumptions
- Reference Sources
- U.S. Bureau of Labor Statistics work-year definition (2,080 hours)
- IRS employer tax guide
- Precision Guarantee
- All converted values to 2 decimal places
- Edge Cases Tested
- Non-standard hours per week, zero salary
Inflation Calculator
- Formula
- Adjusted Value = Original × (1 + rate)^years; Purchasing Power = Original / (1 + rate)^years
- Reference Sources
- U.S. Bureau of Labor Statistics CPI data
- Federal Reserve inflation methodology
- Precision Guarantee
- Adjusted value to 2 decimal places; cumulative inflation to 4 decimal places
- Edge Cases Tested
- Zero inflation, negative inflation (deflation), single year
Tip Calculator
- Formula
- Tip = Bill × Rate; Per Person = (Bill + Tip) / Split Count
- Reference Sources
- Standard U.S. tipping conventions (15%, 18%, 20%, 25%)
- Precision Guarantee
- All amounts to 2 decimal places with proper rounding
- Edge Cases Tested
- Zero tip, single person split, very large party
Currency Converter
- Formula
- Converted = Amount × Exchange Rate
- Reference Sources
- Exchange rates from exchangerate-api.com (updated daily)
- Precision Guarantee
- Converted amounts to 2 decimal places; exchange rates to 6 decimal places
- Edge Cases Tested
- Same currency conversion, zero amount, rate of 1.0
Found an error?
If you find a calculation that does not match a trusted reference source, please contact us immediately. We take accuracy reports seriously and will investigate within 24 hours. Include the calculator name, your inputs, the expected result, and the reference source you used for comparison.