Method and sources
How DepositFX calculates a two-currency comparison
This page explains the calculation model, the direction of the exchange rate, the role of the reference table and the limits of the result. It is an editorial explanation of the tool, not a bank quote or a recommendation.
1. What the calculator is comparing
DepositFX compares two hypothetical fixed-deposit paths using the same starting amount and term. The first path keeps the money in the currency already held. The second path converts that amount into another currency, applies a user-entered or reference deposit rate, and converts the maturity amount back to the original currency. The comparison is useful for seeing how interest and exchange-rate movement interact; it does not predict a future rate.
2. Calculation model
The current calculator uses simple interest. For each path, the estimated interest is the principal multiplied by the annual rate and the term in months divided by 12.
interest = principal × annual rate × months ÷ 12maturity amount = principal + interestcomparison result in base currency = comparison maturity amount × maturity exchange rateThe model does not compound interest. If a product quotes an effective or compounded annual return, enter a rate that represents the product convention and verify the result against the bank's own disclosure.
3. Worked example
Assume a user holds CNY 100,000, compares a 1.5% CNY deposit with a 4% USD deposit for 12 months, and enters an exchange rate of 7.20 CNY per USD. The CNY path estimates CNY 101,500 at maturity. The USD path starts with USD 13,888.89, estimates USD 14,444.44 at maturity, and converts that amount back at 7.20 to about CNY 104,000. Under these assumptions, the difference is about CNY 2,500.
If the maturity rate is 7.00 instead, the converted USD result is about CNY 101,111, which is below the CNY path. At 7.40, it is about CNY 106,889, which is higher. These are scenarios, not forecasts. The threshold rate is the line at which the two estimated maturity values are equal.
4. Exchange-rate direction and spread
Always read the unit shown beside the rate. A quote such as “1 USD = 7.20 CNY” means that one USD is exchanged for 7.20 CNY. Reversing the quote changes the calculation. Banks and platforms may also use different buy and sell rates. The optional spread field is a rough way to represent that cost; it cannot reproduce every fee, markup or timing difference in a real transaction.
5. Reference rates and source policy
The source table links to public bank pages selected as representative references for the listed currency. Each row includes a checked date. A reference rate is a starting point for a calculation, not a guarantee that the same rate is available to every customer. Product eligibility, minimum balance, term, tax treatment, deposit insurance, fees and early-withdrawal rules can change.
When a source page changes or a reader reports an outdated link, the correction can be sent through the contact page. We do not claim that the table is real-time, and users should confirm the final quote with the bank's official website, app or branch.
6. What is outside the model
- Taxes, withholding, account fees, transfer fees and intermediary charges.
- Deposit insurance limits, customer eligibility and product availability.
- Early withdrawal, renewal, compounding and changing rates during the term.
- Slippage between the displayed exchange rate and the rate actually executed.
- Any prediction of where a currency or interest rate will move next.
7. Editorial updates
The calculator logic and explanatory pages are maintained as a small independent project. We aim to keep formulas visible, distinguish estimates from facts, link to primary bank pages and show checked dates for reference rates. Changes to calculation logic or source coverage should be described in the page or repository rather than hidden behind an unexplained result.