diff --git a/sonyflake/new_id.go b/sonyflake/new_id.go
new file mode 100644
index 0000000..b25ce85
--- /dev/null
+++ b/sonyflake/new_id.go
@@ -0,0 +1,43 @@
+package sonyflake
+
+import (
+	"errors"
+	"time"
+)
+
+// NewIdByTime generates a unique ID by time.
+// After the Sonyflake time overflows, NewIdByTime returns an error.
+// Less than Sonyflake min time, NewIdByTime returns an error.
+func (sf *Sonyflake) NewIdByTime(t time.Time) (int64, error) {
+	if t.UnixNano() < DefaultStartTime.UnixNano() {
+		return 0, errors.New("min date is 2015/01/01")
+	}
+	const maskSequence = uint16(1<<BitLenSequence - 1)
+
+	sf.mutex.Lock()
+	defer sf.mutex.Unlock()
+
+	current := currentElapsedTimeWithNow(t, sf.startTime)
+	if sf.elapsedTime < current {
+		sf.elapsedTime = current
+		sf.sequence = 0
+	} else { // sf.elapsedTime >= current
+		sf.sequence = (sf.sequence + 1) & maskSequence
+		if sf.sequence == 0 {
+			sf.elapsedTime++
+			overtime := sf.elapsedTime - current
+			time.Sleep(sleepTimeWithNow(t, overtime))
+		}
+	}
+
+	return sf.toID()
+}
+
+func sleepTimeWithNow(t time.Time, overtime int64) time.Duration {
+	return time.Duration(overtime)*10*time.Millisecond -
+		time.Duration(t.UTC().UnixNano()%sonyflakeTimeUnit)*time.Nanosecond
+}
+
+func currentElapsedTimeWithNow(t time.Time, startTime int64) int64 {
+	return toSonyflakeTime(t) - startTime
+}
diff --git a/sonyflake/sonyflake.go b/sonyflake/sonyflake.go
index 17a376b..7a04b43 100644
--- a/sonyflake/sonyflake.go
+++ b/sonyflake/sonyflake.go
@@ -22,7 +22,7 @@ const (
 	sonyflakeTimeUnit = 1e7 // nsec, i.e. 10 msec
 )
 
-var DefaultStartTime = time.Date(2020, 10, 1, 0, 0, 0, 0, time.UTC)
+var DefaultStartTime = time.Date(2015, 1, 1, 0, 0, 0, 0, time.UTC)
 
 // Sonyflake is a distributed unique ID generator.
 type Sonyflake struct {