Compared to the same time period last year, revenue increased 52.3% to $413.4 million in the third quarter, while earnings per diluted share rose 22.3% to $3.56.
The number of independent active earning OPTAVIA Coaches exceeded 61,000 at the end of the third quarter, with growth of 44.9% from the same period last year and up 3% sequentially.
New client numbers are up about 50% year-over-year in the month of September due to the essential start promotion and the continued strong demand for our coach supported health and wellness plan.
As a result of new client acquisition, productivity hit a record high for the company with revenue per active earning coach reaching $6,773.
This is up 7% from a year ago and up 1.7% from Q2, the prior high.
Through mid-October, there have been over 217,000 unique downloads and daily average usage has averaged approximately 50,000 over the past month.
And that recently went live with approximately 2,000 business leaders and business coaches and will be rolled out across the broader coach population of 61,000-plus OPTAVIA coaches during the fourth quarter.
We found that 66% of adults say having support helped them throughout their health and wellness journey and that more than four in five or 81% of U.S. adults believe that they would be more successful in creating healthy habits if they had support from someone who had been in their shoes.
About 91.9% of our revenue is subscription-based and 100% of our orders are DTC, ships directly to consumers.
In 2019, I shared the goal with our investment community of Medifast generating $1 billion in revenue by the end of 2021.
In Q3, we are pleased to announce we surpassed that full year revenue goal three months ahead of the original projection, allowing OPTAVIA to join an elite group of brands as it exceeded $1 billion in annual revenue.
According to a study by the Boston Consulting Group, there are around 290 $1 billion FMCG brands with U.S. sales and only around 20 of those brands were introduced after the year 2000.
Today, OPTAVIA joins that select group of $1 billion brands.
Revenue in the third quarter of 2021 increased 52.3% to $413.4 million from $271.5 million in the third quarter of 2020, reflecting continued growth in the number of active earning OPTAVIA coaches and higher per coach productivity.
We ended the quarter with over 61,000 active earning OPTAVIA coaches, another new record, up 3% sequentially compared to Q2 and an increase of 44.9% from last year's third quarter.
Average revenue per active earning OPTAVIA Coach for the third quarter was 6,773, also a new record and a 1.7% higher than the previous record set in Q2 of 2021.
Versus a year ago, revenue per active earning OPTAVIA Coach was up 7%.
Gross profit for the third quarter of 2021 increased 50.5% to $307.1 million compared to $204 million in the prior year period, primarily as a result of increased revenue, partially offset by increased cost of sales.
Gross profit margin was 74.3%, down 90 basis points compared to 75.2% in the third quarter of 2020.
SG&A expenses for the third quarter of 2021 increased 57.9% to $251.9 million compared to $159.5 million for the third quarter of 2020.
SG&A as a percentage of revenue increased 220 basis points year-over-year to 60.9% versus 58.7% in the third quarter of 2020.
Income from operations increased $10.6 million to $55.2 million from $44.6 million in the prior year period, reflecting higher gross profit, partially offset by increased SG&A expenses.
Income from operations as a percentage of revenue was 13.3% for the quarter compared to 16.4% in the same period last year.
The effective tax rate was 23.9% for the third quarter of 2021 compared to 22.8% in last year's third quarter, reflecting higher state income tax rates and limitations on deductibility of officer compensation along with the tax benefit of stock compensation.
Net income in the third quarter of 2021 was $42 million or $3.56 per diluted share based on approximately 11.8 million shares of common stock outstanding.
This compares to net income of $34.5 million or $2.91 per diluted share based on approximately 11.9 million shares of common stock outstanding in last year's third quarter.
With approximately $160 million of cash, cash equivalents and investment securities and no interest-bearing debt, our balance sheet remains strong.
It's also important to note that we have been steadily increasing our share buyback activity, including repurchasing $26.3 million of stock in the third quarter, bringing the total for the first nine months of 2021 to approximately $46 million.
Finally, in September 2021, our Board of Directors declared a quarterly cash dividend of $16.6 million or $1.42 per share, which is payable on November 8, 2021, to stockholders of record as of September 21, 2021.
For the full year 2021, we expect revenue to be in the range of $1.51 billion to $1.53 billion and diluted earnings per share to be in the range of $13.27 to $13.96.
Our guidance also assumes a 23.25% to 24.25% effective tax rate.
We continue to target 15% top line growth and 15% operating income margin in the long term, and we remain confident in our ability to deliver long-term sustainable growth at those levels.

Summary:
Compared to the same time period last year, revenue increased 52.3% to $413.4 million in the third quarter, while earnings per diluted share rose 22.3% to $3.56.
Revenue in the third quarter of 2021 increased 52.3% to $413.4 million from $271.5 million in the third quarter of 2020, reflecting continued growth in the number of active earning OPTAVIA coaches and higher per coach productivity.
Net income in the third quarter of 2021 was $42 million or $3.56 per diluted share based on approximately 11.8 million shares of common stock outstanding.
For the full year 2021, we expect revenue to be in the range of $1.51 billion to $1.53 billion and diluted earnings per share to be in the range of $13.27 to $13.96.