Methodology and Data Sources
Currency conversion
What data is used
Currency exchange rates are fetched in real time from an external API provider via a serverless function (/.netlify/functions/convert). The rate returned is a mid-market reference rate for the queried currency pair at the time of the request.
How the calculation works
The formula is straightforward: converted amount = input amount × exchange rate. The rate is fetched server-side and returned to the browser, where multiplication happens client-side.
What the rate represents
The displayed rate is a market reference, not a bank or card network rate. When you actually exchange money, your provider adds spread, fees, or both. The difference between reference rate and execution rate can range from under 0.5% (competitive transfer services) to 3% or more (airport exchanges, some card networks with dynamic conversion). This calculator does not include those costs.
Limitations
- Rates are indicative and update per request; they are not streamed in real time.
- Weekend and holiday rates may reflect the last available market quote.
- The tool does not model card network fees, remittance charges, intermediary bank costs, or tax implications.
- For accounting close, treasury operations, or compliance, use your organization's approved rate source and policy.
Time zone conversion
How it works
Time zone conversions use the Luxon library with IANA timezone identifiers (e.g. America/New_York, Europe/Paris). The user's input is treated as a local datetime in the source zone, then transformed to the target zone. This is date-aware, meaning DST transitions are handled automatically.
Time code parsing
The time-code converter parses natural-language expressions (e.g. "2pm EDT", "tomorrow 15:00 CET") by extracting the timezone abbreviation, mapping it to an IANA zone via a fixed table, resolving relative date words, then constructing a timezone-aware datetime.
Limitations
- Timezone abbreviations are globally ambiguous in some cases (CST can mean US Central or China Standard Time). This tool uses a fixed mapping table for consistency.
- Very informal phrases may not parse reliably. Including a date improves accuracy.
- The tool does not check public holidays, working-hour policies, or calendar conflicts.
- For legal or contractual deadlines, verify with official jurisdiction rules.
Crypto profit and loss estimation
What data is used
Historical crypto prices are fetched from the CoinGecko API via /.netlify/functions/crypto-convert. The rate returned is a daily reference price for the queried asset and fiat pair on the specified date.
How the calculation works
For each transaction row: estimated P/L = (sell date rate − buy date rate) × amount. Both rates are fetched individually and the arithmetic runs client-side.
What is not included
- Trading fees, slippage, and exchange-specific spreads
- Intraday price variation (only daily reference rates are used)
- Gas fees, staking rewards, or DeFi yields
- Tax lot identification methods (FIFO, LIFO, HIFO)
- Jurisdiction-specific tax rules, exemptions, or filing requirements
This tool is designed for planning and scenario comparison. Treat output as a directional estimate and reconcile with exchange records and professional tax guidance for official purposes.
Browser-based math, pricing, and date calculators
How they work
Percentage, VAT, loan payment, date difference, age, and unit conversion tools use deterministic formulas that run directly in the browser. In these cases, the page uses your entered values together with transparent arithmetic or calendar logic rather than calling an external pricing feed.
What that means in practice
- Percentage and VAT outputs are formula-based reference calculations.
- Loan payment estimates use standard amortization math and optional extra-payment simulation.
- Date and age tools use browser-side calendar arithmetic with date-only comparisons.
- Unit conversion uses fixed conversion factors and formula transforms for the selected measurement family.
Limitations
- Tax-related pages are practical estimators, not legal or filing guidance.
- Loan outputs do not include lender fees, insurance, taxes, or jurisdiction-specific disclosure rules unless explicitly stated.
- Date-based tools are strong for planning, but contractual deadlines may depend on local legal interpretation, cutoff times, or custom calendars.
- Unit conversion factors are standardized references and should be validated against domain-specific requirements where rounding tolerance matters.
General principles
- Privacy: most calculations run client-side in the browser. Serverless functions fetch reference data but do not store user inputs or results.
- No accounts required: all tools are free to use without registration.
- Transparency: each tool page includes visible methodology, limitations, and data source notes.
- No financial advice: Toolsified is a utility platform, not a financial advisor, broker, or tax authority.