diff --git a/fixed.go b/fixed.go
new file mode 100644
index 0000000..09b62d1
--- /dev/null
+++ b/fixed.go
@@ -0,0 +1,29 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type Fixed struct {
+	duration time.Duration
+	next     time.Time
+}
+
+func NewFixed(duration time.Duration) (*Fixed, error) {
+	if duration < 0 {
+		return nil, fmt.Errorf("invalid duration, must be >= 0")
+	}
+	return &Fixed{
+		duration: duration,
+		next:     time.Now().Add(duration),
+	}, nil
+}
+
+func (f *Fixed) Next() time.Time {
+	now := time.Now()
+	if now.After(f.next) {
+		f.next = f.next.Add(f.duration)
+	}
+	return f.next
+}
diff --git a/schedule.go b/schedule.go
new file mode 100644
index 0000000..964d9e8
--- /dev/null
+++ b/schedule.go
@@ -0,0 +1,7 @@
+package main
+
+import "time"
+
+type Schedule interface {
+	Next() time.Time
+}