diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
index 895a9e83b6a89..db12f89bf2dd1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
@@ -484,11 +484,11 @@ private static void FormatCustomized<TChar>(
                         tokenLen = ParseRepeatPattern(format, i, ch);
                         if (tokenLen <= MaxSecondsFractionDigits)
                         {
-                            long fraction = (dateTime.Ticks % Calendar.TicksPerSecond);
-                            fraction /= (long)Math.Pow(10, 7 - tokenLen);
+                            int fraction = (int)(dateTime.Ticks % Calendar.TicksPerSecond);
+                            fraction /= TimeSpanParse.Pow10UpToMaxFractionDigits(MaxSecondsFractionDigits - tokenLen);
                             if (ch == 'f')
                             {
-                                FormatFraction(ref result, (int)fraction, fixedNumberFormats[tokenLen - 1]);
+                                FormatFraction(ref result, fraction, fixedNumberFormats[tokenLen - 1]);
                             }
                             else
                             {
@@ -507,7 +507,7 @@ private static void FormatCustomized<TChar>(
                                 }
                                 if (effectiveDigits > 0)
                                 {
-                                    FormatFraction(ref result, (int)fraction, fixedNumberFormats[effectiveDigits - 1]);
+                                    FormatFraction(ref result, fraction, fixedNumberFormats[effectiveDigits - 1]);
                                 }
                                 else
                                 {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
index 687cafbe9ca50..9613bddf43549 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
@@ -3179,6 +3179,7 @@ internal static bool ParseDigits(ref __DTString str, int minDigitLen, int maxDig
 
         private static bool ParseFractionExact(ref __DTString str, int maxDigitLen, scoped ref double result)
         {
+            Debug.Assert(maxDigitLen <= DateTimeFormat.MaxSecondsFractionDigits);
             if (!str.GetNextDigit())
             {
                 str.Index--;
@@ -3197,7 +3198,7 @@ private static bool ParseFractionExact(ref __DTString str, int maxDigitLen, scop
                 result = result * 10 + str.GetDigit();
             }
 
-            result /= TimeSpanParse.Pow10(digitLen);
+            result /= TimeSpanParse.Pow10UpToMaxFractionDigits(digitLen);
             return digitLen == maxDigitLen;
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
index 8c8bea12bbf6b..48faa5b1a9834 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs
@@ -311,7 +311,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
             int seconds = (int)(time / TimeSpan.TicksPerSecond % 60);
             int fraction = (int)(time % TimeSpan.TicksPerSecond);
 
-            long tmp;
+            int tmp;
             int i = 0;
             int tokenLen;
 
@@ -356,8 +356,8 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
-                        DateTimeFormat.FormatFraction(ref result, (int)tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
+                        tmp /= TimeSpanParse.Pow10UpToMaxFractionDigits(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[tokenLen - 1]);
                         break;
                     case 'F':
                         //
@@ -370,7 +370,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
 
                         tmp = fraction;
-                        tmp /= TimeSpanParse.Pow10(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
+                        tmp /= TimeSpanParse.Pow10UpToMaxFractionDigits(DateTimeFormat.MaxSecondsFractionDigits - tokenLen);
                         int effectiveDigits = tokenLen;
                         while (effectiveDigits > 0)
                         {
@@ -386,7 +386,7 @@ private static void FormatCustomized<TChar>(TimeSpan value, scoped ReadOnlySpan<
                         }
                         if (effectiveDigits > 0)
                         {
-                            DateTimeFormat.FormatFraction(ref result, (int)tmp, DateTimeFormat.fixedNumberFormats[effectiveDigits - 1]);
+                            DateTimeFormat.FormatFraction(ref result, tmp, DateTimeFormat.fixedNumberFormats[effectiveDigits - 1]);
                         }
                         break;
                     case 'd':
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
index c900e64dcb969..033d0abe4e904 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanParse.cs
@@ -47,6 +47,7 @@
 //
 ////////////////////////////////////////////////////////////////////////////
 
+using System.Buffers.Text;
 using System.Diagnostics;
 using System.Text;
 
@@ -114,7 +115,7 @@ public bool NormalizeAndValidateFraction()
                 if (_zeroes == 0 && _num > MaxFraction)
                     return false;
 
-                int totalDigitsCount = ((int)Math.Floor(Math.Log10(_num))) + 1 + _zeroes;
+                int totalDigitsCount = FormattingHelpers.CountDigits((uint)_num) + _zeroes;
 
                 if (totalDigitsCount == MaxFractionDigits)
                 {
@@ -132,7 +133,7 @@ public bool NormalizeAndValidateFraction()
                     // .000001  normalize to 10 ticks
                     // .1       normalize to 1,000,000 ticks
 
-                    _num *= (int)Pow10(MaxFractionDigits - totalDigitsCount);
+                    _num *= Pow10UpToMaxFractionDigits(MaxFractionDigits - totalDigitsCount);
                     return true;
                 }
 
@@ -143,7 +144,18 @@ public bool NormalizeAndValidateFraction()
                 // .099999999   normalize to 1,000,000 ticks
 
                 Debug.Assert(_zeroes > 0); // Already validated that in the condition _zeroes == 0 && _num > MaxFraction
-                _num = (int)Math.Round((double)_num / Pow10(totalDigitsCount - MaxFractionDigits), MidpointRounding.AwayFromZero);
+
+                if (_zeroes > MaxFractionDigits)
+                {
+                    // If there are 8 leading zeroes, it rounds to zero
+                    _num = 0;
+                    return true;
+                }
+
+                Debug.Assert(totalDigitsCount - MaxFractionDigits <= MaxFractionDigits);
+                uint power = (uint)Pow10UpToMaxFractionDigits(totalDigitsCount - MaxFractionDigits);
+                // Unsigned integer division, rounding away from zero
+                _num = (int)(((uint)_num + power / 2) / power);
                 Debug.Assert(_num < MaxFraction);
 
                 return true;
@@ -563,20 +575,21 @@ internal bool SetBadFormatSpecifierFailure(char? formatSpecifierCharacter = null
             }
         }
 
-        internal static long Pow10(int pow)
+        internal static int Pow10UpToMaxFractionDigits(int pow)
         {
-            return pow switch
-            {
-                0 => 1,
-                1 => 10,
-                2 => 100,
-                3 => 1000,
-                4 => 10000,
-                5 => 100000,
-                6 => 1000000,
-                7 => 10000000,
-                _ => (long)Math.Pow(10, pow),
-            };
+            ReadOnlySpan<int> powersOfTen =
+            [
+                1,
+                10,
+                100,
+                1000,
+                10000,
+                100000,
+                1000000,
+                10000000,
+            ];
+            Debug.Assert(powersOfTen.Length == MaxFractionDigits + 1);
+            return powersOfTen[pow];
         }
 
         private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)