diff --git a/libcxx/include/__chrono/duration.h b/libcxx/include/__chrono/duration.h
--- a/libcxx/include/__chrono/duration.h
+++ b/libcxx/include/__chrono/duration.h
@@ -343,6 +343,8 @@
     return __duration_eq<duration<_Rep1, _Period1>, duration<_Rep2, _Period2> >()(__lhs, __rhs);
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 // Duration !=
 
 template <class _Rep1, class _Period1, class _Rep2, class _Period2>
@@ -354,6 +356,8 @@
     return !(__lhs == __rhs);
 }
 
+#endif // _LIBCPP_STD_VER <= 17
+
 // Duration <
 
 template <class _LhsDuration, class _RhsDuration>
@@ -417,6 +421,19 @@
     return !(__lhs < __rhs);
 }
 
+#if _LIBCPP_STD_VER >= 20
+
+template<class _Rep1, class _Period1, class _Rep2, class _Period2>
+  requires three_way_comparable<typename _Ct::rep>
+inline _LIBCPP_HIDE_FROM_ABI
+constexpr auto operator<=>(const duration<Rep1, Period1>& __lhs,
+                           const duration<Rep2, Period2>& __rhs)
+{
+    return _Ct(lhs).count() <=> _Ct(rhs).count();
+}
+
+#endif // _LIBCPP_STD_VER >= 20
+
 // Duration +
 
 template <class _Rep1, class _Period1, class _Rep2, class _Period2>
diff --git a/libcxx/include/chrono b/libcxx/include/chrono
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -182,7 +182,7 @@
    bool operator==(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
-   bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
+   bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); // removed in C++20
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
    bool operator< (const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
@@ -195,6 +195,10 @@
 template <class Rep1, class Period1, class Rep2, class Period2>
    constexpr
    bool operator>=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
+template<class Rep1, class Period1, class Rep2, class Period2>
+  requires three_way_comparable<typename CT::rep>
+  constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
+                             const duration<Rep2, Period2>& rhs);                           // since C++20
 
 // duration_cast
 template <class ToDuration, class Rep, class Period>
diff --git a/libcxx/test/std/time/time.duration/time.duration.comparisons/compare.three_way.pass.cpp b/libcxx/test/std/time/time.duration/time.duration.comparisons/compare.three_way.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/time/time.duration/time.duration.comparisons/compare.three_way.pass.cpp
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <chrono>
+
+// duration
+
+// template<class Rep1, class Period1, class Rep2, class Period2>
+//     requires ThreeWayComparable<typename CT::rep>
+//   constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
+//                              const duration<Rep2, Period2>& rhs);
+
+#include <cassert>
+#include <chrono>
+
+#include "test_comparisons.h"
+
+int main(int, char**) {
+    {
+    constexpr std::chrono::seconds s1(3);
+    constexpr std::chrono::seconds s2(3);
+    static_assert((s1 <=> s2) == std::strong_ordering::equal);
+    static_assert(testOrder(s1, s2, std::strong_ordering::equal));
+    }
+    {
+    constexpr std::chrono::seconds s1(3);
+    constexpr std::chrono::seconds s2(4);
+    static_assert((s1 <=> s2) == std::strong_ordering::less);
+    static_assert(testOrder(s1, s2, std::strong_ordering::less));
+    }
+    {
+    constexpr std::chrono::milliseconds s1(3);
+    constexpr std::chrono::microseconds s2(3000);
+    static_assert((s1 <=> s2) == std::strong_ordering::equal);
+    static_assert(testOrder(s1, s2, std::strong_ordering::equal));
+    }
+    {
+    constexpr std::chrono::milliseconds s1(3);
+    constexpr std::chrono::microseconds s2(4000);
+    static_assert((s1 <=> s2) == std::strong_ordering::less);
+    static_assert(testOrder(s1, s2, std::strong_ordering::less));
+    }
+    {
+    constexpr std::chrono::duration<int, std::ratio<2, 3>> s1(9);
+    constexpr std::chrono::duration<int, std::ratio<3, 5>> s2(10);
+    static_assert((s1 <=> s2) == std::strong_ordering::equal);
+    static_assert(testOrder(s1, s2, std::strong_ordering::equal));
+    }
+    {
+    constexpr std::chrono::duration<int, std::ratio<2, 3>> s1(10);
+    constexpr std::chrono::duration<int, std::ratio<3, 5>> s2(9);
+    static_assert((s1 <=> s2) == std::strong_ordering::greater);
+    static_assert(testOrder(s1, s2, std::strong_ordering::greater));
+    }
+    {
+    constexpr std::chrono::duration<int, std::ratio<2, 3>> s1(9);
+    constexpr std::chrono::duration<double, std::ratio<3, 5>> s2(10);
+    static_assert((s1 <=> s2) == std::strong_ordering::equal);
+    static_assert(testOrder(s1, s2, std::strong_ordering::equal));
+    }
+
+  return 0;
+}