For the third quarter, we delivered revenue above the high end of the range of the outlook we provided with total revenue ending the quarter at $181.3 million.
Third quarter adjusted EBITDA was $75.3 million, representing an adjusted EBITDA margin of 42%, exceeding just the high end of our outlook.
Our Q3 maintenance and annual rate of 88% was above the low to mid-80% renewal rate we noted we expected in 2021.
In Q3, our subscription revenue grew at a 20% year-over-year rate with subscription ARR growing 23% year over year.
That execution led to another quarter of better-than-expected financial results for the third quarter with total revenue ending at $181.3 million, above the high end of our total revenue outlook of about $176 million to $180 million.
Total license and maintenance revenue was $149 million in the third quarter, which is a decrease of 6% from the prior year period.
The maintenance revenue was $120 million in the third quarter, which is up slightly from the prior year.
On a trailing 12-month basis, our maintenance renewal rate is 89%.
Also consistent with recent quarters, we want to provide the in-quarter renewal rate for the third quarter, which currently stands at approximately 88%, which again is above our expectations at the start of the year.
For the third quarter, license revenue was $29.2 million, which represents a decline of approximately 26% as compared to the third quarter of 2020.
Third quarter subscription revenue was $32.3 million, up the 20% year over year.
Total ARR have reached approximately $624 million as of September 30, 2021, reflecting year-over-year growth of 9% and is up slightly from our ending Q2 2021 ARR balance of $621 million, which is the corrected amount included in our 8-K filing from earlier this month.
Our subscription ARR of $130.2 million increased 23% year over year and 9% sequentially from the second quarter.
So we finished the third quarter of 2021 with 786 customers that have spent more than $100,000 with us in the last 12 months, which is a 4% improvement over the previous year.
Third quarter adjusted EBITDA was $75.3 million, representing an adjusted EBITDA margin of 42%, exceeding the high end of the outlook for the third quarter despite continuing to invest in our business.
Excluded from the adjusted EBITDA are onetime costs of approximately of the $2.9 million of cyber-related remediation, containment, investigation, and professional fees, net of insurance proceeds.
Net leverage at September 30 was approximately 3.8 times our pro forma trailing 12-month adjusted EBITDA.
We retained the full amount of the $1.9 billion in term debt that the company had at present.
During the third quarter, we completed a two for one reverse stock split and declared a dividend of $1.50 per share on this post-split basis, which was paid in August.
In addition, N-able repaid $325 million of inter-company debt.
As a result of this repayment, our cash balance is $709 million at the end of the third quarter, bringing our net debt to approximately $1.2 billion.
For the fourth quarter of 2021, we expect total revenue to be in the range of $180 million to $184 million, representing a year-over-year decline of negative 3% to negative 1%.
Adjusted EBITDA for the fourth quarter is expected to be approximately $72 million to $74 million, which also implies an approximately 40% adjusted EBITDA margin.
Non-GAAP fully diluted earnings per share is projected to be $0.25 to $0.26 per share, assuming an estimated 160.7 million fully diluted shares outstanding, which reflects the reverse stock split completed on July 30.
And finally, our outlook for the fourth quarter assumes a non-GAAP tax rate of 22%, and that we expect to pay approximately $8 million in cash taxes during the fourth quarter of 2021.
For the full year, we expect total revenue to be in the range of $712 million to $716 million, representing a year-over-year decline of negative 1% to flat with prior year.
So our adjusted EBITDA for the full year is expected to be approximately $297 million to $299 million, which implies an approximately 42% adjusted EBITDA margin for the year.
Non-GAAP fully diluted earnings per share is projected to be $1.14 to $1.15 per share, assuming an estimated 160.5 million fully diluted shares outstanding.

Summary:
That execution led to another quarter of better-than-expected financial results for the third quarter with total revenue ending at $181.3 million, above the high end of our total revenue outlook of about $176 million to $180 million.
For the fourth quarter of 2021, we expect total revenue to be in the range of $180 million to $184 million, representing a year-over-year decline of negative 3% to negative 1%.
Non-GAAP fully diluted earnings per share is projected to be $0.25 to $0.26 per share, assuming an estimated 160.7 million fully diluted shares outstanding, which reflects the reverse stock split completed on July 30.
For the full year, we expect total revenue to be in the range of $712 million to $716 million, representing a year-over-year decline of negative 1% to flat with prior year.
Non-GAAP fully diluted earnings per share is projected to be $1.14 to $1.15 per share, assuming an estimated 160.5 million fully diluted shares outstanding.