The cost of a BA Same Day Flight Change depends on the ticket fare purchased. For flexible fares, same-day changes are often free of charge. However, passengers with non-flexible or discounted fares may need to pay a fee, which varies by route and fare type. It’s advisable to check the terms and conditions of your specific ticket or contact British Airways customer service to confirm any charges associated with changing your flight. Keep in mind that additional fare differences may apply if the new flight is more expensive than the original one.