Purchasing Power Calculator

This Purchasing Power Calculator helps you compare value over time, translate value across currencies using PPP, and estimate housing buying power given income and financing assumptions. Use the CPI/index method when you have published index values, or the compound-rate method when you want to apply an average annual inflation rate.

Results are estimates for planning and comparison. Where possible, supply official series (CPI or PPP conversion factors) from national statistics offices or international sources for best accuracy. The housing estimator solves for a house price consistent with a user-specified debt-to-income constraint and includes property tax, insurance, and HOA assumptions.

Updated Nov 1, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 1e9e293dad2a • Reviewed by Fidamen Standards Committee

Calculation method

Uses user-supplied CPI (or price index) values to scale an amount directly by index ratios.

Inputs

Amount

Min 0.01

From year

Min 1800 · Max 2100

To year

Min 1800 · Max 2100

Annual inflation rate (%, compound)

Min -50 · Max 100

From CPI / price index value

Min 0.0001

To CPI / price index value

Min 0.0001

PPP conversion factor (origin: local currency per international dollar)

Min 0.0001

PPP conversion factor (target: local currency per international dollar)

Min 0.0001

Origin currency codeTarget currency codeAnnual gross income

Min 0

Available down payment

Min 0

Mortgage annual interest rate (%)

Min 0 · Max 100

Mortgage term (years)

Min 1 · Max 50

Other monthly debt payments

Min 0

Maximum debt-to-income ratio (%) used for housing

Min 1 · Max 100

Annual property tax rate (% of house price)

Min 0

Annual home insurance cost

Min 0

HOA / condo fees (monthly)

Min 0

Results

Updates as you type

Inflation-adjusted amount

$1,771.78

Index ratio (to/from)

1.7718

Output	Value	Unit
Inflation-adjusted amount	$1,771.78	USD
Index ratio (to/from)	1.7718	—

Primary result$1,771.78

Visualization

Points

Methodology

CPI/index method: the amount is scaled by the ratio of the destination index to the origin index (amount * to_index / from_index). This is the preferred approach when official index series are available for the same currency and price concept.

Compound-rate method: applies an annualized compound factor: amount * (1 + rate)^(years). Use this when you have an average annual inflation expectation rather than index series.

PPP conversion: converts via PPP conversion factors expressed as 'local currency per international dollar' for each economy. Conversion multiplies the origin amount by (ppp_to / ppp_from) to represent equivalent purchasing power in the target currency.

Housing estimate: solves for the maximum house price P that satisfies allowed monthly payment = mortgage payment on (P - down_payment) + monthly property taxes + insurance + HOA. The mortgage payment is computed using the standard fixed-rate amortization formula. See 'How is calculated' for the algebraic rearrangement.

F.A.Q.

How accurate are these results?

These outputs are estimates. Accuracy depends on input quality: official CPI indices, published PPP conversion factors, and actual mortgage rates. Use official series where available and treat compound-rate results as scenario estimates rather than precise historical reconstructions. See citations for data sources and standards on numerical validation. Results do not include transaction costs, taxes on sale, or behavioral changes.

Which method should I use for time comparisons?

Prefer the CPI/index method when you have consistent index values for both dates (same index series). Use the compound-rate method when you only have an average annual rate or for forward-looking scenarios.

Where do I get CPI and PPP data?

Obtain CPI series from national statistical offices or central banks and PPP conversion factors from international organizations. When using third-party data, verify series definitions and coverage. The tool accepts user-supplied values only and does not fetch live data.

Are there regulatory or safety considerations?

This tool is informational only. For regulated activities (e.g., consumer lending calculations, disclosures), consult applicable local rules. Numerical and software practices referenced follow standards and good practices listed in the citations; use audited data and professional advice for compliance-sensitive decisions.

What are the tool limits and known failure modes?

Known limits include: division by zero if indices or factors are zero, loss of precision for extremely large exponents, and inappropriate use of PPP factors across non-comparable baskets. The housing solver assumes taxes scale with house price and a fixed-rate mortgage. For zero or negative interest rates, formulas may need special handling; validate results and run sensitivity checks.

How should I calibrate or validate results?

Cross-check with official series (e.g., published CPI ratios or PPP tables) for sample dates. For housing estimates, validate against lender affordability calculators and use quoted mortgage rates from lenders. Maintain versioned records of inputs when auditing calculations.

Sources & citations

NIST: Frameworks and guidance on software assurance and numeric validation — https://www.nist.gov/
ISO standards on data quality and information accuracy — https://www.iso.org/
IEEE guidance on software engineering and reproducible computations — https://www.ieee.org/
OSHA guidance on workplace well-being (context for financial-health tools) — https://www.osha.gov/
Official CPI and inflation statistics (example national statistics office) — https://www.bls.gov/
International PPP data and methodology (example international data provider) — https://data.worldbank.org/indicator/PA.NUS.PPP
CFPB — Consumer Financial Protection Bureau — https://www.consumerfinance.gov/
Federal Reserve — Consumer Credit — https://www.federalreserve.gov/releases/g19/current/
IRS Publication 17 — Your Federal Income Tax — https://www.irs.gov/publications/p17

Further resources

Related tools

External guidance

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: 1e9e293dad2a

What changed (latest)

v1.0.0 • 2025-11-01 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

Governance

Last updated: Nov 1, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
MINOR: New features or fields that do not change existing outputs for the same inputs.
PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

Verify formulas and unit definitions against primary standards or datasets.
Run golden-case regression suite and edge-case suite.
Record reviewer sign-off with credentials and scope.
Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

Uses exact unit definitions from the Fidamen conversion library.
Internal calculations use double precision; display rounding follows the unit's configured decimal places.
Not a substitute for calibrated instruments in regulated contexts.
Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-01 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 090c8499479e