Metric always seemed a bit timeless to me, which might explain why it freaks me out that the Canadian band has been together for nearly two decades. How have they managed to continue headlining theaters like the McDonald even as fellow Canadian contemporaries like Broken Social Scene and Stars faded from view?

I’d pinpoint three primary reasons: First, there’s the sound, which over time has evolved gracefully from the tightly-wound post-punk of the band’s debut to the dance-floor synth pop of the last few records. While Metric has never released a perfect record (2009’s Fantasies comes close), every one of their five LPs packs at least a handful of bangers, from “Dead Disco” on the debut, “Help, I’m Alive” from Fantasies and “The Shade” from the most recent release, Pagans in Vegas.

This leads nicely into reason two: Metric is a killer live act. Certainly the four members, who have yet to experience a lineup change, have developed plenty of live interplay during their many years playing together. But most credit is due to lead singer Emily Haines, who approaches each show with the swagger of a woman who has been commanding stages since the Clinton administration.

Finally, like any lasting band, they pack a number of unexpected strengths. Take Haines and guitarist James Shaw’s acoustic take on fan favorite “Gimme Sympathy.” The track beautifully demonstrates that even when stripped of the disco beats and shimmering synths, Metric still maintains its power — one grounded in Haines’ earthy, multi-faceted voice and the band’s penchant for writing songs that never go quite where you expect them.

New York-based indie-pop outfit Joywave opens for Metric 8 pm Saturday, Feb. 20, at the McDonald Theatre; $26 adv., $31 door.