Index: include/cmath
===================================================================
--- include/cmath
+++ include/cmath
@@ -296,6 +296,10 @@
 float          truncf(float x);
 long double    truncl(long double x);
 
+constexpr float       lerp(float a,       float b,       float t);
+constexpr double      lerp(double a,      double b,      double t);
+constexpr long double lerp(long double a, long double b, long double t);
+
 }  // std
 
 */
@@ -606,6 +610,31 @@
     return isfinite(__lcpp_x);
 }
 
+#if _LIBCPP_STD_VER > 17
+
+_LIBCPP_INLINE_VISIBILITY
+_LIBCPP_CONSTEXPR float
+lerp(float __a, float __b, float __t)
+{
+    return (1 - __t) * __a + __t * __b;
+}
+
+_LIBCPP_INLINE_VISIBILITY
+_LIBCPP_CONSTEXPR double
+lerp(double __a, double __b, double __t)
+{
+    return (1 - __t) * __a + __t * __b;
+}
+
+_LIBCPP_INLINE_VISIBILITY
+_LIBCPP_CONSTEXPR long double
+lerp(long double __a, long double __b, long double __t)
+{
+    return (1 - __t) * __a + __t * __b;
+}
+
+#endif // _LIBCPP_STD_VER > 17
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP_CMATH
Index: test/std/numerics/c.math/lerp.pass.cpp
===================================================================
--- /dev/null
+++ test/std/numerics/c.math/lerp.pass.cpp
@@ -0,0 +1,64 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++98, c++03, c++11, c++14, c++17
+
+// cmath
+
+// constexpr float       lerp(float a,       float b,       float t);
+// constexpr double      lerp(double a,      double b,      double t);
+// constexpr long double lerp(long double a, long double b, long double t);
+
+#include "test_macros.h"
+
+#include <cmath>
+
+void test_double()
+{
+    constexpr double a = 4;
+    constexpr double b = 0;
+    constexpr double t = 0.25;
+    constexpr double r = 3;
+    
+    constexpr auto res = std::lerp(a, b, t);
+    static_assert(res == r);
+    ASSERT_SAME_TYPE(decltype(t), decltype(res));
+}
+
+void test_long_double()
+{
+    constexpr long double a = 4;
+    constexpr long double b = 0;
+    constexpr long double t = 0.25;
+    constexpr long double r = 3;
+    
+    constexpr auto res = std::lerp(a, b, t);
+    static_assert(res == r);
+    ASSERT_SAME_TYPE(decltype(t), decltype(res));
+}
+
+void test_float()
+{
+    constexpr float a = 4;
+    constexpr float b = 0;
+    constexpr float t = 0.25;
+    constexpr float r = 3;
+    
+    constexpr auto res = std::lerp(a, b, t);
+    static_assert(res == r);
+    ASSERT_SAME_TYPE(decltype(t), decltype(res));
+}
+
+int main(int, char**)
+{
+    test_double();
+    test_long_double();
+    test_float();
+    
+    return 0;
+}
\ No newline at end of file
Index: www/cxx2a_status.html
===================================================================
--- www/cxx2a_status.html
+++ www/cxx2a_status.html
@@ -141,7 +141,7 @@
 	<tr><td><a href="https://wg21.link/P0339R6">P0339R6</a></td><td>LWG</td><td>polymorphic_allocator<> as a vocabulary type</td><td>Kona</td><td></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P0340R3">P0340R3</a></td><td>LWG</td><td>Making std::underlying_type SFINAE-friendly</td><td>Kona</td><td></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P0738R2">P0738R2</a></td><td>LWG</td><td>I Stream, You Stream, We All Stream for istream_iterator</td><td>Kona</td><td></td><td></td></tr>
-	<tr><td><a href="https://wg21.link/P0811R3">P0811R3</a></td><td>LWG</td><td>Well-behaved interpolation for numbers and pointers</td><td>Kona</td><td></td><td></td></tr>
+	<tr><td><a href="https://wg21.link/P0811R3">P0811R3</a></td><td>LWG</td><td>Well-behaved interpolation for numbers and pointers</td><td>Kona</td><td>Complete</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P0920R2">P0920R2</a></td><td>LWG</td><td>Precalculated hash values in lookup</td><td>Kona</td><td></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P1001R2">P1001R2</a></td><td>LWG</td><td>Target Vectorization Policies from Parallelism V2 TS to C++20</td><td>Kona</td><td></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P1024R3">P1024R3</a></td><td>LWG</td><td>Usability Enhancements for std::span</td><td>Kona</td><td>Complete</td><td>9.0</td></tr>