# Currency converter

> Convert between 160 currencies at the latest daily reference rates, with the rate date and a 90-day history chart.

Interactive version: https://www.calcopenly.com/finance/currency-converter
Subject: Finance calculators

Convert an amount between about 160 currencies at the latest daily reference rates. Rates come from the ExchangeRate-API open-access feed, with the European Central Bank's reference rates (via Frankfurter) as the fallback; the page shows which source and date it used.

The conversion itself is computed in 50-digit decimal from the two currencies' rates against the US dollar, and the result is rounded to the target currency's minor unit (two decimals for most, none for the yen). A quick-reference table lists common amounts in both directions, and a chart shows the last 90 days for currency pairs the ECB publishes.

These are mid-market rates. Banks and card networks add a margin, so the amount you are charged will usually be lower than shown.

## Inputs

- **Amount**
- **From**
- **To**
- **Rate (1 from = ? to)**

## Results

- Converted — main result
- Inverse rate

## Worked examples

### 100 at 83.5

- Amount: 100
- From: USD
- To: INR
- Rate (1 from = ? to): 83.5
- **Converted: 8,350.00**
- **Inverse rate: 0.011976**
- Checked against: 100 × 83.5; 1/83.5

### Zero amount

- Amount: 0
- From: USD
- To: INR
- Rate (1 from = ? to): 1.1
- **Converted: 0.00**
- Checked against: 0 × rate

### Half-cent rounding

- Amount: 3
- From: USD
- To: INR
- Rate (1 from = ? to): 0.335
- **Converted: 1.00**
- **Inverse rate: 2.98507**
- Checked against: 3 × 0.335 = 1.005 → 1.00 half-even; 1/0.335

## Questions

### How often are the exchange rates updated?

The rate feed updates once a day, and the page shows the time of the last update. The app keeps the most recent rates on your device and fetches new ones when the saved copy is more than 12 hours old, so conversions keep working offline with the last known rates.

### Why is my bank's rate different?

The rates here are mid-market reference rates, halfway between buying and selling prices. Banks, card networks and exchange bureaus add a margin to that rate and some add a fixed fee, so the rate on your statement will differ.

### Which currencies have a history chart?

The 90-day chart uses the European Central Bank's reference rates, published for about 30 currencies including USD, EUR, GBP, INR, JPY, CNY, AUD and CAD. Pairs involving other currencies, such as AED or SAR, show a note instead of a chart.

### How accurate is the currency converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “100 at 83.5” is checked against 100 × 83.5; 1/83.5.

### Where does the method come from?

ExchangeRate-API open access endpoint (daily rates); Frankfurter — European Central Bank reference rates.

## Sources

- [ExchangeRate-API open access endpoint (daily rates)](https://www.exchangerate-api.com/docs/free)
- [Frankfurter — European Central Bank reference rates](https://frankfurter.dev/)

_Note: financial information, not professional advice._