Try AddDate:
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
then := now.AddDate(0, -1, 0)
fmt.Println("then:", then)
}
Produces:
now: 2009-11-10 23:00:00 +0000 UTC
then: 2009-10-10 23:00:00 +0000 UTC
Playground: http://play.golang.org/p/QChq02kisT