Start with whether you are buying or selling cash

Receiving foreign notes for a trip means buying foreign currency as the customer. Returning leftover notes for won means selling it. Read the customer-facing cash buying or selling column; the bank’s side of the transaction is the reverse.

The Bank of Korea’s exchange-rate lesson (Korean) distinguishes a reference rate from customer rates. This guide covers reading quotes and doing arithmetic, rather than forecasting rates. Source link checked on 4 November 2026.

Match the quotation unit as well as the currency

Won per US dollar and won per 100 yen are different units. Record the currency code, quoted quantity, time, and whether the price is for cash or a transfer. Multiplying without checking the quoted quantity changes the result.

Won cost = foreign amount / quoted quantity × applied rate + separate charges

A transfer rate or card conversion rate prices a different transaction. Keep it out of a cash-only comparison.

Apply a discount to an illustrative spread

These are teaching figures, not current rates or a bank offer. Assume a reference of KRW 1,400 per foreign unit, an added cash spread of KRW 20, and a 90% discount on that spread.

Before discount: 1,400 + 20 = KRW 1,420
Remaining spread: 20 × (1 − 0.90) = KRW 2
Applied price: 1,400 + 2 = KRW 1,402
Receiving 500 units: 500 × 1,402 = KRW 701,000

This differs from reducing the entire purchase price by 90%. Check eligible transactions, limits, separate charges, and rounding in the provider’s actual terms.

Work backwards from a won budget

With a budget of KRW 701,000, no separate charge, and the same illustrative price of KRW 1,402, the arithmetic result is 500 foreign units. Where the calculation produces fractions, ask how the available banknotes and any remainder will be handled.

Arithmetic foreign amount = (won budget − separate charges) / applied rate × quoted quantity

Keep a short record before exchanging

  1. Write the currency code and whether you are buying or selling cash.
  2. Check the quoted quantity, applied rate, and separate charges at the same time.
  3. Calculate the won paid and foreign cash received, then compare them with the final quote.
  4. Confirm collection place, date, denominations, and cancellation terms; keep the receipt.

The calculations explain a cost structure. Use the provider’s final amounts for a real transaction.