diff --git a/goextVersion.go b/goextVersion.go
index 3dddc2d..9d52344 100644
--- a/goextVersion.go
+++ b/goextVersion.go
@@ -1,5 +1,5 @@
 package goext
 
-const GoextVersion = "0.0.480"
+const GoextVersion = "0.0.481"
 
-const GoextVersionTimestamp = "2024-07-02T11:32:22+0200"
+const GoextVersionTimestamp = "2024-07-04T16:24:49+0200"
diff --git a/timeext/diff.go b/timeext/diff.go
new file mode 100644
index 0000000..118dadc
--- /dev/null
+++ b/timeext/diff.go
@@ -0,0 +1,13 @@
+package timeext
+
+import "time"
+
+func YearDifference(t1 time.Time, t2 time.Time, tz *time.Location) float64 {
+
+	yDelta := float64(t1.Year() - t2.Year())
+
+	processT1 := float64(t1.Sub(TimeToYearStart(t1, tz))) / float64(TimeToYearEnd(t1, tz).Sub(TimeToYearStart(t1, tz)))
+	processT2 := float64(t2.Sub(TimeToYearStart(t2, tz))) / float64(TimeToYearEnd(t2, tz).Sub(TimeToYearStart(t2, tz)))
+
+	return yDelta + (processT1 - processT2)
+}
diff --git a/timeext/diff_test.go b/timeext/diff_test.go
new file mode 100644
index 0000000..79cbf4d
--- /dev/null
+++ b/timeext/diff_test.go
@@ -0,0 +1,83 @@
+package timeext
+
+import (
+	"math"
+	"testing"
+	"time"
+)
+
+func TestYearDifferenceWithSameYearAndDay(t *testing.T) {
+	t1 := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	t2 := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	expected := 0.0
+	result := YearDifference(t1, t2, time.UTC)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceWithOneYearApart(t *testing.T) {
+	t1 := time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)
+	t2 := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	expected := 1.0
+	result := YearDifference(t1, t2, time.UTC)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceWithDifferentMonths(t *testing.T) {
+	t1 := time.Date(2020, 6, 1, 0, 0, 0, 0, time.UTC)
+	t2 := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	expected := 0.4166666666666667 // Approximation of 5/12 months
+	result := YearDifference(t1, t2, time.UTC)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceAcrossYears(t *testing.T) {
+	t1 := time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)
+	t2 := time.Date(2020, 6, 1, 0, 0, 0, 0, time.UTC)
+	expected := 0.5833333333333334 // Approximation of 7/12 months
+	result := YearDifference(t1, t2, time.UTC)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceWithTimezone(t *testing.T) {
+	tz, _ := time.LoadLocation("America/New_York")
+	t1 := time.Date(2021, 1, 1, 0, 0, 0, 0, tz)
+	t2 := time.Date(2020, 6, 1, 0, 0, 0, 0, tz)
+	expected := 0.5833333333333334 // Same as UTC but ensuring timezone is considered
+	result := YearDifference(t1, t2, tz)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceWithNegativeDifference(t *testing.T) {
+	t1 := time.Date(2020, 1, 1, 0, 0, 0, 0, TimezoneBerlin)
+	t2 := time.Date(2021, 1, 1, 0, 0, 0, 0, TimezoneBerlin)
+	expected := -1.0
+	result := YearDifference(t1, t2, TimezoneBerlin)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestYearDifferenceWithNegativeDifference2(t *testing.T) {
+	t1 := time.Date(2020, 7, 1, 0, 0, 0, 0, TimezoneBerlin)
+	t2 := time.Date(2021, 7, 1, 0, 0, 0, 0, TimezoneBerlin)
+	expected := -1.0
+	result := YearDifference(t1, t2, TimezoneBerlin)
+	if !epsilonEquals(result, expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func epsilonEquals(a, b float64) bool {
+	epsilon := 0.01
+	return math.Abs(a-b) < epsilon
+}
diff --git a/timeext/time.go b/timeext/time.go
index 517f02a..1b0b168 100644
--- a/timeext/time.go
+++ b/timeext/time.go
@@ -65,6 +65,10 @@ func TimeToYearEnd(t time.Time, tz *time.Location) time.Time {
 	return TimeToYearStart(t, tz).AddDate(1, 0, 0).Add(-1)
 }
 
+func TimeToNextYearStart(t time.Time, tz *time.Location) time.Time {
+	return TimeToYearStart(t, tz).AddDate(1, 0, 0)
+}
+
 // IsSameDayIncludingDateBoundaries returns true if t1 and t2 are part of the same day (TZ/Berlin), the boundaries of the day are
 // inclusive, this means 2021-09-15T00:00:00 is still part of the day 2021-09-14
 func IsSameDayIncludingDateBoundaries(t1 time.Time, t2 time.Time, tz *time.Location) bool {
diff --git a/timeext/time_test.go b/timeext/time_test.go
index df45868..2aed255 100644
--- a/timeext/time_test.go
+++ b/timeext/time_test.go
@@ -72,6 +72,13 @@ func TestIsSunday(t *testing.T) {
 	}
 }
 
+func TestIsSunday_OnSunday(t *testing.T) {
+	sunday := time.Date(2022, 5, 15, 0, 0, 0, 0, TimezoneBerlin) // A Sunday
+	if !IsSunday(sunday, TimezoneBerlin) {
+		t.Errorf("Expected true for Sunday")
+	}
+}
+
 func TestDurationFromTime(t *testing.T) {
 	expected := time.Duration(13*time.Hour + 14*time.Minute + 15*time.Second)
 	result := DurationFromTime(13, 14, 15)
@@ -156,3 +163,31 @@ func TestAddYears(t *testing.T) {
 		t.Errorf("Expected %v but got %v", expected, result)
 	}
 }
+
+func TestIsDatePartEqual_SameDateDifferentTimes(t *testing.T) {
+	tz := time.UTC
+	t1 := time.Date(2022, 5, 18, 10, 30, 0, 0, tz)
+	t2 := time.Date(2022, 5, 18, 20, 45, 0, 0, tz)
+	if !IsDatePartEqual(t1, t2, tz) {
+		t.Errorf("Expected dates to be equal")
+	}
+}
+
+func TestWithTimePart_ChangeTime(t *testing.T) {
+	base := time.Date(2022, 5, 18, 0, 0, 0, 0, time.UTC)
+	result := WithTimePart(base, 15, 30, 45)
+	expected := time.Date(2022, 5, 18, 15, 30, 45, 0, time.UTC)
+	if !result.Equal(expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}
+
+func TestCombineDateAndTime_CombineDifferentParts(t *testing.T) {
+	date := time.Date(2022, 5, 18, 0, 0, 0, 0, time.UTC)
+	timePart := time.Date(2000, 1, 1, 15, 30, 45, 0, time.UTC)
+	result := CombineDateAndTime(date, timePart)
+	expected := time.Date(2022, 5, 18, 15, 30, 45, 0, time.UTC)
+	if !result.Equal(expected) {
+		t.Errorf("Expected %v, got %v", expected, result)
+	}
+}