diff --git a/cache_test.go b/cache_test.go
index 161f0a4..cea110b 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -4,16 +4,45 @@ import (
 	"bytes"
 	"crypto/rand"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"log"
 	mrand "math/rand"
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 )
 
+// mockTimer is a mock for Timer contract.
+type mockTimer struct {
+	nowCallsCnt uint32        // stores the number of times Now() was called
+	nowCallback func() uint32 // callback to be executed inside Now()
+}
+
+// Now mock logic.
+func (mock *mockTimer) Now() uint32 {
+	atomic.AddUint32(&mock.nowCallsCnt, 1)
+	if mock.nowCallback != nil {
+		return mock.nowCallback()
+	}
+
+	return uint32(time.Now().Unix())
+}
+
+// SetNowCallback sets the callback to be executed inside Now().
+// You can control the return value this way.
+func (mock *mockTimer) SetNowCallback(callback func() uint32) {
+	mock.nowCallback = callback
+}
+
+// nowCallsCount returns the number of times Now() was called.
+func (mock *mockTimer) NowCallsCount() int {
+	return int(atomic.LoadUint32(&mock.nowCallsCnt))
+}
+
 func TestFreeCache(t *testing.T) {
 	cache := NewCache(1024)
 	if cache.HitRate() != 0 {
@@ -229,20 +258,135 @@ func TestExpire(t *testing.T) {
 }
 
 func TestTTL(t *testing.T) {
-	cache := NewCache(1024)
-	key := []byte("abcd")
-	val := []byte("efgh")
-	err := cache.Set(key, val, 2)
+	t.Run("with no expire key", testTTLWithNoExpireKey)
+	t.Run("with expire key, not yet expired", testTTLWithNotYetExpiredKey)
+	t.Run("with expire key, expired", testTTLWithExpiredKey)
+	t.Run("with not found key", testTTLWithNotFoundKey)
+}
+
+func testTTLWithNoExpireKey(t *testing.T) {
+	t.Parallel()
+
+	// arrange
+	var now uint32 = 1659954367
+	timer := new(mockTimer)
+	timer.SetNowCallback(func() uint32 {
+		return now
+	})
+	cache := NewCacheCustomTimer(512*1024, timer)
+	key := []byte("test-key")
+	value := []byte("this key does not expire")
+	expireSeconds := 0
+	if err := cache.Set(key, value, expireSeconds); err != nil {
+		t.Fatalf("prerequisite failed: could not set the key to query ttl for: %v", err)
+	}
+
+	// act
+	ttl, err := cache.TTL(key)
+
+	// assert
 	if err != nil {
-		t.Error("err should be nil", err.Error())
+		t.Errorf("expected nil, but got %v", err)
 	}
-	time.Sleep(time.Second)
+	if ttl != uint32(expireSeconds) {
+		t.Errorf("expected %d, but got %d ", expireSeconds, ttl)
+	}
+	if timer.NowCallsCount() != 1 {
+		t.Errorf("expected %d, but got %d ", 1, timer.NowCallsCount())
+	}
+}
+
+func testTTLWithNotYetExpiredKey(t *testing.T) {
+	t.Parallel()
+
+	// arrange
+	var now uint32 = 1659954368
+	timer := new(mockTimer)
+	timer.SetNowCallback(func() uint32 {
+		return now
+	})
+	cache := NewCacheCustomTimer(512*1024, timer)
+	key := []byte("test-key")
+	value := []byte("this key expires, but is not expired")
+	expireSeconds := 300
+	if err := cache.Set(key, value, expireSeconds); err != nil {
+		t.Fatalf("prerequisite failed: could not set the key to query ttl for: %v", err)
+	}
+
+	// act
 	ttl, err := cache.TTL(key)
+
+	// assert
 	if err != nil {
-		t.Error("err should be nil", err.Error())
+		t.Errorf("expected nil, but got %v", err)
 	}
-	if ttl != 1 {
-		t.Fatalf("ttl should be 1, but %d returned", ttl)
+	if ttl != uint32(expireSeconds) {
+		t.Errorf("expected %d, but got %d ", expireSeconds, ttl)
+	}
+	if timer.NowCallsCount() != 2 { // one call from set, one from ttl
+		t.Errorf("expected %d, but got %d ", 2, timer.NowCallsCount())
+	}
+}
+
+func testTTLWithExpiredKey(t *testing.T) {
+	t.Parallel()
+
+	// arrange
+	var now uint32 = 1659954369
+	expireSeconds := 600
+	timer := new(mockTimer)
+	timer.SetNowCallback(func() uint32 {
+		switch timer.NowCallsCount() {
+		case 1:
+			return now
+		case 2:
+			return now + uint32(expireSeconds)
+		}
+
+		return now
+	})
+	cache := NewCacheCustomTimer(512*1024, timer)
+	key := []byte("test-key")
+	value := []byte("this key is expired")
+	if err := cache.Set(key, value, expireSeconds); err != nil {
+		t.Fatalf("prerequisite failed: could not set the key to query ttl for: %v", err)
+	}
+
+	// act
+	ttl, err := cache.TTL(key)
+
+	// assert
+	if !errors.Is(err, ErrNotFound) {
+		t.Errorf("expected %v, but got %v", ErrNotFound, err)
+	}
+	if ttl != 0 {
+		t.Errorf("expected %d, but got %d ", 0, ttl)
+	}
+	if timer.NowCallsCount() != 2 { // one call from set, one from ttl
+		t.Errorf("expected %d, but got %d ", 2, timer.NowCallsCount())
+	}
+}
+
+func testTTLWithNotFoundKey(t *testing.T) {
+	t.Parallel()
+
+	// arrange
+	timer := new(mockTimer)
+	cache := NewCacheCustomTimer(512*1024, timer)
+	key := []byte("test-not-found-key")
+
+	// act
+	ttl, err := cache.TTL(key)
+
+	// assert
+	if !errors.Is(err, ErrNotFound) {
+		t.Errorf("expected %v, but got %v", ErrNotFound, err)
+	}
+	if ttl != 0 {
+		t.Errorf("expected %d, but got %d ", 0, ttl)
+	}
+	if timer.NowCallsCount() != 0 {
+		t.Errorf("expected %d, but got %d ", 0, timer.NowCallsCount())
 	}
 }
 
@@ -804,6 +948,35 @@ func BenchmarkHashFunc(b *testing.B) {
 	}
 }
 
+func benchmarkTTL(expireSeconds int) func(b *testing.B) {
+	return func(b *testing.B) {
+		cache := NewCache(512 * 1024)
+		key := []byte("bench-ttl-key")
+		value := []byte("bench-ttl-value")
+		if err := cache.Set(key, value, expireSeconds); err != nil {
+			b.Fatalf("prerequisite failed: could not set the key to query TTL for: %v", err)
+		}
+
+		b.ReportAllocs()
+		b.ResetTimer()
+
+		for i := 0; i < b.N; i++ {
+			_, err := cache.TTL(key)
+			if err != nil {
+				b.Error(err)
+			}
+		}
+	}
+}
+
+func BenchmarkTTL_withKeyThatDoesNotExpire(b *testing.B) {
+	benchmarkTTL(0)(b)
+}
+
+func BenchmarkTTL_withKeyThatDoesExpire(b *testing.B) {
+	benchmarkTTL(30)(b)
+}
+
 func TestConcurrentGetTTL(t *testing.T) {
 	cache := NewCache(256 * 1024 * 1024)
 	primaryKey := []byte("hello")
diff --git a/segment.go b/segment.go
index 9ebea9b..bcc90a9 100644
--- a/segment.go
+++ b/segment.go
@@ -170,7 +170,7 @@ func (seg *segment) touch(key []byte, hashVal uint64, expireSeconds int) (err er
 	hdr := (*entryHdr)(unsafe.Pointer(&hdrBuf[0]))
 
 	now := seg.timer.Now()
-	if hdr.expireAt != 0 && hdr.expireAt <= now {
+	if isExpired(hdr.expireAt, now) {
 		seg.delEntryPtr(slotId, slot, idx)
 		atomic.AddInt64(&seg.totalExpired, 1)
 		err = ErrNotFound
@@ -208,7 +208,7 @@ func (seg *segment) evacuate(entryLen int64, slotId uint8, now uint32) (slotModi
 			seg.vacuumLen += oldEntryLen
 			continue
 		}
-		expired := oldHdr.expireAt != 0 && oldHdr.expireAt < now
+		expired := isExpired(oldHdr.expireAt, now)
 		leastRecentUsed := int64(oldHdr.accessTime)*atomic.LoadInt64(&seg.totalCount) <= atomic.LoadInt64(&seg.totalTime)
 		if expired || leastRecentUsed || consecutiveEvacuate > 5 {
 			seg.delEntryPtrByOffset(oldHdr.slotId, oldHdr.hash16, oldOff)
@@ -292,7 +292,7 @@ func (seg *segment) locate(key []byte, hashVal uint64, peek bool) (hdr *entryHdr
 	hdr = (*entryHdr)(unsafe.Pointer(&hdrBuf[0]))
 	if !peek {
 		now := seg.timer.Now()
-		if hdr.expireAt != 0 && hdr.expireAt <= now {
+		if isExpired(hdr.expireAt, now) {
 			seg.delEntryPtr(slotId, slot, idx)
 			atomic.AddInt64(&seg.totalExpired, 1)
 			err = ErrNotFound
@@ -328,18 +328,19 @@ func (seg *segment) ttl(key []byte, hashVal uint64) (timeLeft uint32, err error)
 		return
 	}
 	ptr := &slot[idx]
-	now := seg.timer.Now()
 
 	var hdrBuf [ENTRY_HDR_SIZE]byte
 	seg.rb.ReadAt(hdrBuf[:], ptr.offset)
 	hdr := (*entryHdr)(unsafe.Pointer(&hdrBuf[0]))
 
 	if hdr.expireAt == 0 {
-		timeLeft = 0
-		return
-	} else if hdr.expireAt != 0 && hdr.expireAt >= now {
-		timeLeft = hdr.expireAt - now
 		return
+	} else {
+		now := seg.timer.Now()
+		if !isExpired(hdr.expireAt, now) {
+			timeLeft = hdr.expireAt - now
+			return
+		}
 	}
 	err = ErrNotFound
 	return
@@ -477,3 +478,8 @@ func (seg *segment) getSlot(slotId uint8) []entryPtr {
 	slotOff := int32(slotId) * seg.slotCap
 	return seg.slotsData[slotOff : slotOff+seg.slotLens[slotId] : slotOff+seg.slotCap]
 }
+
+// isExpired checks if a key is expired.
+func isExpired(keyExpireAt, now uint32) bool {
+	return keyExpireAt != 0 && keyExpireAt <= now
+}