(Authors Note: This was originally written in February 2015. The situation for Syrian military armor has taken a turn drastically for the worse since that time. The uptick in ATGM proliferation and the capture of SAA armor should be looked, especially in the context of the offensives in Idlib, Hama, Aleppo, and Daraa)
As the most tank-heavy military in the Middle East, by a heavy percentage, the SAA entered the Syrian Civil War with a tremendous amount of armor. Open source numbers put their pre-war numbers at roughly 4,500 Main Battle Tanks (2,000 T-55, 1,000 T-62, 1,500 T-72), 2,000 BMPs (almost entirely BMP-1s, though the Republican Guard boasted some 100 BMP-2s), 4,731 other armored vehicles (including self propelled AA, self propelled, artillery, armored cars, APCs, and armored AA missile platforms), along with 2,518 transport and logistics trucks, and unknown thousands of jeeps and small vehicles. Of these, a large number of vehicles are either mothballed, broken down for parts, or simply inoperable, with many conflict experts saying the real number of MBTs at the outset of the conflict was 2,500, BMPs at roughly 1,000, and the remainder an unknown entity. Even still, this number of armored vehicles is an enormous amount that outpaces most other military forces in the world (at the start of the conflict, Syria had the 5th largest tank army in the world).
In four years of war, most notably the last three, the number of main battle tanks has shrunk by nearly half with conflict blogger Oryx claiming that of 2,500 MBTs,roughly 1,500 remain
 as of November 2014 and of the estimated 1,000 BMP-1s in service, Oryx claims that 350 have been destroyed
 and approximately 175 captured by the opposition, as of January 2015. With over half of the BMP fleet, a mainstay of SAA battle doctrine, destroyed or captured, and approaching half of all MBTs destroyed or captured, how much longer can the SAA sustain these losses before the armored strength of the SAA is depleted and more tanks and armored vehicles exist in opposition hands than the government? My rough estimate: 2 years.
In 2015 alone, there have been roughly 100 ATGM strikes on Syrian armor (spread between tanks, APCs, and heavy equipment like bulldozers). From posts on this subreddit alone, I’ve counted 65 ATGM (all types) strikes since February just here on the forums, but that doesn’t account for how many of those strikes weren’t catastrophic hits. Here is a post with 32 strikes from between Feb 10 and Mar 19
 . Roughly 100 tanks and BMPs have been struck by an ATGM. An untold number have been destroyed by another tank, or destroyed by other AT means (RPGs, AT cannon, mines, IEDs, SVBIED. If I had to guess I would add 20+ to that number of tanks damaged or destroyed since January, based solely on recollection of video and photos of tanks being destroyed by other means. As far as captured…
Several BMP-1s were captured at Brigade 82 in late January, along with a ZSU-23-4 quad barreled 23mm AA vehicle, and two AA missile vehicles. In Feburary, a T-72 and two BMP-1s were captured in Daraa area during the offensive. In Aleppo, a BMP-1 and a T-72, and two T-55s were captured by Islamic Front during that counter attacks, (Bashkuy specifically). In March, I didn’t keep good track of what has been captured, although I know in Idlib at least two BMP-1s, two armored cars (BRDM-2 I think), and a small number of logistics trucks were captured. Most recently (a few days ago), a T-72 and three BMP-1s were captured from Hezbollah/SAA forces in the Qalamoun (might have that wrong, it might be Qunaitirah).
The SAA has been losing vehicles at an alarming rate, with approximately 138 vehicles captured, destroyed, or damaged by opposition offensives, ATGM strikes, tank on tank, or other AT weapons. Given the combined 2,000 tanks + BMPs remaining in the Syrian inventory, if losses were to continue at this rate, the SAA can sustain approximately four more years of fighting before the entire tank inventory is used up (without massive replenishment). Of course in reality, if tank losses continue at this rate, replacing them on the battlefield will become a question of retaining enough for defense in secured areas, or continuing to atrophy over the long term through destruction and capture. It is likely that two more years of this rate of destruction would reduce Syrian tank inventory by at least half, and require massive rearmament by an outside power (such as a former Soviet state which has not made the same agreements as Russia with regards to not supplying Syria with more tanks).