diff --git a/fgprof.go b/fgprof.go
index 31871c8..2716e6c 100644
--- a/fgprof.go
+++ b/fgprof.go
@@ -14,6 +14,8 @@ import (
 // that needs to be invoked by the caller to stop the profiling and write the
 // results to w using the given format.
 func Start(w io.Writer, format Format) func() error {
+	startTime := time.Now()
+
 	// Go's CPU profiler uses 100hz, but 99hz might be less likely to result in
 	// accidental synchronization with the program we're profiling.
 	const hz = 99
@@ -39,7 +41,13 @@ func Start(w io.Writer, format Format) func() error {
 
 	return func() error {
 		stopCh <- struct{}{}
-		return writeFormat(w, stackCounts.HumanMap(prof.SelfFrame()), format, hz)
+		return writeFormat(
+			w,
+			stackCounts.HumanMap(prof.SelfFrame()),
+			format,
+			hz,
+			startTime,
+		)
 	}
 }
 
diff --git a/format.go b/format.go
index c9bfe9f..053d4d5 100644
--- a/format.go
+++ b/format.go
@@ -5,6 +5,7 @@ import (
 	"io"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/google/pprof/profile"
 )
@@ -21,12 +22,12 @@ const (
 	FormatPprof Format = "pprof"
 )
 
-func writeFormat(w io.Writer, s map[string]int, f Format, hz int) error {
+func writeFormat(w io.Writer, s map[string]int, f Format, hz int, startTime time.Time) error {
 	switch f {
 	case FormatFolded:
 		return writeFolded(w, s)
 	case FormatPprof:
-		return toPprof(s, hz).Write(w)
+		return toPprof(s, hz, startTime).Write(w)
 	default:
 		return fmt.Errorf("unknown format: %q", f)
 	}
@@ -42,7 +43,7 @@ func writeFolded(w io.Writer, s map[string]int) error {
 	return nil
 }
 
-func toPprof(s map[string]int, hz int) *profile.Profile {
+func toPprof(s map[string]int, hz int, startTime time.Time) *profile.Profile {
 	functionID := uint64(1)
 	locationID := uint64(1)
 	line := int64(1)