In United Kingdom, "I Think I'm in Love with You" debuted at number fifteen on the UK Singles Chart in the week of July 15, 2000, and stayed on the chart for seven weeks. It became her second top twenty single there. In Switzerland, the single debuted at number sixty-one on the issue dated June 25, 2000. In the next week peaked at number forty-one and stayed on the chart for twelve weeks. The single peaked at number three on the Ultratip chart of Belgium's Wallonia region, and number thirty-six on the Belgium Flanders Ultratop 50 chart. It also reached number thirty in Italy. "I Think I'm in Love with You" peaked at number thirty-one on the European Hot 100 Singles chart, as compiled by "Billboard".