There's a 100% chance Amanda Seyfried has (already) been makin' it rain for years!

Going back to North Shore High School ... here is a 18-year-old version of the stunning star looking oh so "fetch" -- playing "Mean Girls" Karen Smith -- in her Santa talent show outfit back in 2004 (left).

And, 19 years later, Mrs. Seyfried recently dazzled and glowed on stage at a skincare event in Shanghai, China (right). Today, this "Jingle Bell Rock" queen is celebrating her 38th birthday, and she's never shined brighter!

"What a bright time, it's the right time!"

The question is ...