As the final season of Game of Thrones begins, fans are looking back over everything that has happened since that very first episode... and wondering exactly how much time has passed in Westeros. Over the course of the past seven seasons, multiple major characters have lost their lives, wars have been fought and lost over the Iron Throne, the Starks have made it to the furthest reaches of Westeros and back to Winterfell, and the White Walker threat has gone from a scary story to a terrifying reality. So how much time did all that actually take? Based on what we know, about six to seven years.
Unfortunately, it's not immediately obvious how time is passing in the world of Game of Thrones - this is not a world that follows an easy timeline. Fans aren't able to look at the kinds of markers that work for other TV shows, as the people of Westeros don't celebrate American holidays (no Christmas special at King's Landing here!), nor are the seasons the same as they are in our world. In addition, the events aren't all happening concurrently, and the issues with travel time in this series have been well-documented by angry fans. However, there are a few comments and details that can be used to put together a rough timeline for the show.
In the pilot episode, it is explicitly stated that it has been seventeen years since Robert's Rebellion, while in season 2, it is said that Renly's death happened eighteen years after the Rebellion. This means that between the pilot and "The Ghost of Harrenhal" (season 2, episode 5), about a year has passed. By season 3's "The Bear And The Maiden Fair" (season 3, episode 7), another year has passed, as Talisa states that the War of the Five Kings has been going on for two years (and started with the end of the first season). This means that by the end of the third season, somewhere between two and three years have passed.
From season 4 onward, things seem to get a little murkier, without quite so many clear markers as to how time is passing (and with some weird travel time jumps just to confuse everyone further). However, there are a couple of mentions of the passage of time to help clear things up. When Jaime heads to Dorne to 'rescue' Myrcella, she says that she has been there for three years. She set out for Sunspear in "The Old Gods And The New" (season 2, episode 6), and sees Jaime again toward the end of season 5, which means that three years passed between the middle of season 2 and the middle of season 5. This means that by the end of season 5, around 4-5 years have passed in total.
The passage of time in seasons six and seven gets even more unclear, especially as there are no helpful ages given or pregnancies to follow. However, there is one helpful way of measuring time: the growth of Little Sam (Gilly's baby). Sam was born back in the third episode of season 3 "Walk of Punishment." By the end of season 7, he appears to be around four years old, and while this is an estimate rather than stated as fact, that would mean that the series is maintaining around one year of time passing per season, and that it has been around six or seven years between the pilot episode and the season 7 finale.
Of course, this is still speculative, thanks to the fact that the show doesn't have a very clear timeline with each scene happening concurrently. While it makes some sense for the show to have covered around six to seven years in seven seasons, there are some moments that would work against the timeline laid out here. Sansa gives her age as 13 in season 1, and yet as 14 in season 3 when she is married to Tyrion. That would suggest that only one year has passed between seasons 1 and 3, directly contradicting Talisa's statement only an episode earlier that at least three years have passed - as the War of Five Kings has been going on for two!
However, the truth of the matter is that timelines, while interesting, aren't actually all that necessary in Game of Thrones. This is a fantasy world where seasons last for years, where young teens are wedded and bedded, and where real magic exists. In a world where age and the passage of time is so warped, the lack of a clear timeline actually adds to the strangeness of this universe - although everyone is still hoping that travel time makes a lot more sense in the final season!