"Hollaback Girl" entered the Billboard Hot 100 at number 82 on the issue dated April 2, 2005, and within six weeks of its release, it had reached the top of the chart, becoming Stefani's first and only US number one. It ended the nine-week run of 50 Cent's "Candy Shop" featuring Olivia, and maintained the number-one position for four consecutive weeks. "Hollaback Girl" ranked second on the 2005 Hot 100 year-end chart, being kept from the top spot by Mariah Carey's "We Belong Together". "Hollaback Girl" held the record for most US radio airplays in one week, with 9,582 plays, and maintained this record for over a year before Shakira and Wyclef Jean's "Hips Don't Lie" overtook the position. It peaked at number one on the Billboard Pop 100 chart for eight weeks and at number 15 on the Hot Dance Club Play chart. The song was a crossover success, and reached number four on the Rhythmic Top 40 and number eight on the Hot R&B/Hip-Hop Songs chart.
The song was noted for having a large number of digital downloads, becoming the first single to sell more digital downloads than CDs. In October 2005, "Hollaback Girl" was the first single to ever sell one million digital downloads and later went on to sell a total of 1.2 million downloads. It was certified five-times platinum by the Recording Industry Association of America. It was later re-certified platinum, for the same sales, due to the change of the RIAA certification criteria for singles. On the year-end list for Hot Digital Songs in 2005, "Hollaback Girl" topped the chart.
"Hollaback Girl" was successful in Canada, where the song debuted and peaked at number 12 on the Canadian Singles Chart. However, Graham Henderson, president of the Canadian Recording Industry Association (CRIA), later argued that based on Canada's population relative to the US, the single should have sold around 120,000 copies and that the comparatively lower sales of 25,000 were a sign that the Canadian copyright law should be tightened to discourage non-commercial peer-to-peer file sharing. Columnist Michael Geist disputed the comparison, arguing that the Canadian online music market was still developing. The song was released in Australia on May 23, 2005, debuting at number one on the ARIA Singles Chart, and in Europe on June 6, 2005, reaching number five on the European Hot 100 Singles. In the United Kingdom, however, "Hollaback Girl" did not perform as well as Stefani's previous releases. The song's predecessors, "What You Waiting For?" and "Rich Girl", had both reached number four, while "Hollaback Girl" debuted at number eight, and stalled at the same position the following week. Although its UK success was limited, it remained in the top 40 for an additional 11 weeks. The single was largely successful across Europe, reaching the top five in Austria, Denmark, Germany, and Ireland, and the top 10 in Belgium, Finland, Italy, the Netherlands, Norway, Sweden, and Switzerland.