"Over the Rainbow" debuted at number 88 on the UK Singles Chart in February 2001 and climbed to number 42 in May, becoming Cassidy's first single to chart in the United Kingdom. In Scotland, it reached number 36, giving Cassidy her first top-forty single in that region. It was her highest-charting song in the United Kingdom until 2007, when "What a Wonderful World" reached number one. The song also reached number 27 in Ireland in December, becoming her only top-forty hit in that country.