diff --git a/spec/std/float_printer/ryu_printf_spec.cr b/spec/std/float_printer/ryu_printf_spec.cr
index 02ac2944a37d..3318c26f3265 100644
--- a/spec/std/float_printer/ryu_printf_spec.cr
+++ b/spec/std/float_printer/ryu_printf_spec.cr
@@ -32,66 +32,11 @@ require "./ryu_printf_test_cases"
 
 struct BigFloat
   def to_s_with_range(*, point_range : Range = -3..15)
-    String.build do |io|
-      to_s_with_range(io, point_range: point_range)
-    end
+    to_s_impl(point_range: point_range, int_trailing_zeros: false)
   end
 
   def to_s_with_range(io : IO, *, point_range : Range = -3..15) : Nil
-    cstr = LibGMP.mpf_get_str(nil, out decimal_exponent, 10, 0, self)
-    length = LibC.strlen(cstr)
-    buffer = Slice.new(cstr, length)
-
-    # add negative sign
-    if buffer[0]? == 45 # '-'
-      io << '-'
-      buffer = buffer[1..]
-      length -= 1
-    end
-
-    point = decimal_exponent
-    exp = point
-    exp_mode = !point_range.includes?(point)
-    point = 1 if exp_mode
-
-    # add leading zero
-    io << '0' if point < 1
-
-    # add integer part digits
-    if decimal_exponent > 0 && !exp_mode
-      # whole number but not big enough to be exp form
-      io.write_string buffer[0, {decimal_exponent, length}.min]
-      buffer = buffer[{decimal_exponent, length}.min...]
-      (point - length).times { io << '0' }
-    elsif point > 0
-      io.write_string buffer[0, point]
-      buffer = buffer[point...]
-    end
-
-    # skip `.0000...`
-    unless buffer.all?(&.=== '0')
-      io << '.'
-
-      # add leading zeros after point
-      if point < 0
-        (-point).times { io << '0' }
-      end
-
-      # add fractional part digits
-      io.write_string buffer
-
-      # print trailing 0 if whole number or exp notation of power of ten
-      if (decimal_exponent >= length && !exp_mode) || ((exp != point || exp_mode) && length == 1)
-        io << '0'
-      end
-    end
-
-    # exp notation
-    if exp_mode
-      io << 'e'
-      io << '+' if exp > 0
-      (exp - 1).to_s(io)
-    end
+    to_s_impl(io, point_range: point_range, int_trailing_zeros: false)
   end
 end
 
diff --git a/spec/std/humanize_spec.cr b/spec/std/humanize_spec.cr
index 1505bcab19d0..abf4213b7887 100644
--- a/spec/std/humanize_spec.cr
+++ b/spec/std/humanize_spec.cr
@@ -93,6 +93,18 @@ describe Number do
     it { assert_prints (-Float64::INFINITY).format, "-Infinity" }
     it { assert_prints Float64::NAN.format, "NaN" }
 
+    it { assert_prints "12345678.90123".to_big_f.format, "12,345,678.90123" }
+    it { assert_prints "12345678.90123".to_big_f.format(decimal_places: 10), "12,345,678.9012300000" }
+    it { assert_prints "12345678.90123".to_big_f.format(decimal_places: -4), "12,350,000" }
+
+    it { assert_prints (2.to_big_f ** 58).format, "288,230,376,151,711,744.0" }
+    it { assert_prints (2.to_big_f ** 58).format(decimal_places: 10), "288,230,376,151,711,744.0000000000" }
+    it { assert_prints (2.to_big_f ** 58).format(decimal_places: -5), "288,230,376,151,700,000" }
+
+    it { assert_prints (2.to_big_f ** -16).format, "0.0000152587890625" }
+    it { assert_prints (2.to_big_f ** -16).format(decimal_places: 20), "0.00001525878906250000" }
+    it { assert_prints (2.to_big_f ** -16).format(decimal_places: 10), "0.0000152588" }
+
     it { assert_prints "12345.67890123456789012345".to_big_d.format, "12,345.67890123456789012345" }
 
     it "extracts integer part correctly (#12997)" do
diff --git a/src/big/big_float.cr b/src/big/big_float.cr
index 5a57500fbdd7..74ce7451a0b5 100644
--- a/src/big/big_float.cr
+++ b/src/big/big_float.cr
@@ -362,6 +362,15 @@ struct BigFloat < Float
   end
 
   def to_s(io : IO) : Nil
+    to_s_impl(io, point_range: -3..15, int_trailing_zeros: true)
+  end
+
+  protected def to_s_impl(*, point_range : Range, int_trailing_zeros : Bool) : String
+    String.build { |io| to_s_impl(io, point_range: point_range, int_trailing_zeros: int_trailing_zeros) }
+  end
+
+  # TODO: refactor into `Float::Printer.shortest`
+  protected def to_s_impl(io : IO, *, point_range : Range, int_trailing_zeros : Bool) : Nil
     cstr = LibGMP.mpf_get_str(nil, out orig_decimal_exponent, 10, 0, self)
     length = LibC.strlen(cstr)
     buffer = Slice.new(cstr, length)
@@ -377,7 +386,7 @@ struct BigFloat < Float
 
     point = decimal_exponent
     exp = point
-    exp_mode = point > 15 || point < -3
+    exp_mode = !point_range.includes?(point)
     point = 1 if exp_mode
 
     # add leading zero
@@ -394,23 +403,27 @@ struct BigFloat < Float
       buffer = buffer[point...]
     end
 
-    io << '.'
+    # omit `.0000...000` if *int_trailing_zeros* is false (used by the
+    # Ryu Printf specs only)
+    if int_trailing_zeros || !buffer.all?(&.=== '0')
+      io << '.'
 
-    # add leading zeros after point
-    if point < 0
-      (-point).times { io << '0' }
-    end
+      # add leading zeros after point
+      if point < 0
+        (-point).times { io << '0' }
+      end
 
-    # add fractional part digits
-    io.write_string buffer
+      # add fractional part digits
+      io.write_string buffer
 
-    # print trailing 0 if whole number or exp notation of power of ten
-    if (decimal_exponent >= length && !exp_mode) || (exp != point && length == 1)
-      io << '0'
+      # print trailing 0 if whole number or exp notation of power of ten
+      if (decimal_exponent >= length && !exp_mode) || ((exp != point || exp_mode) && length == 1)
+        io << '0'
+      end
     end
 
     # exp notation
-    if exp != point
+    if exp_mode
       io << 'e'
       io << '+' if exp > 0
       (exp - 1).to_s(io)
@@ -466,6 +479,27 @@ struct BigFloat < Float
     {% end %}
   end
 
+  # :inherit:
+  def format(io : IO, separator = '.', delimiter = ',', decimal_places : Int? = nil, *, group : Int = 3, only_significant : Bool = false) : Nil
+    number = self
+    if decimal_places
+      number = number.round(decimal_places)
+    end
+
+    if decimal_places && decimal_places >= 0
+      string = number.abs.to_s_impl(point_range: .., int_trailing_zeros: true)
+      integer, _, decimals = string.partition('.')
+    else
+      string = number.to_s_impl(point_range: .., int_trailing_zeros: true)
+      _, _, decimals = string.partition(".")
+      integer = number.trunc.to_big_i.abs.to_s
+    end
+
+    is_negative = number < 0
+
+    format_impl(io, is_negative, integer, decimals, separator, delimiter, decimal_places, group, only_significant)
+  end
+
   def clone
     self
   end
diff --git a/src/humanize.cr b/src/humanize.cr
index e0a5f3f17844..37e129f3bd9d 100644
--- a/src/humanize.cr
+++ b/src/humanize.cr
@@ -56,10 +56,23 @@ struct Number
       integer, _, decimals = string.partition('.')
     end
 
+    is_negative = number.is_a?(Float::Primitive) ? Math.copysign(1, number) < 0 : number < 0
+
+    format_impl(io, is_negative, integer, decimals, separator, delimiter, decimal_places, group, only_significant)
+  end
+
+  # :ditto:
+  def format(separator = '.', delimiter = ',', decimal_places : Int? = nil, *, group : Int = 3, only_significant : Bool = false) : String
+    String.build do |io|
+      format(io, separator, delimiter, decimal_places, group: group, only_significant: only_significant)
+    end
+  end
+
+  private def format_impl(io, is_negative, integer, decimals, separator, delimiter, decimal_places, group, only_significant) : Nil
     int_size = integer.size
     dec_size = decimals.size
 
-    io << '-' if number.is_a?(Float::Primitive) ? Math.copysign(1, number) < 0 : number < 0
+    io << '-' if is_negative
 
     start = int_size % group
     start += group if start == 0
@@ -91,13 +104,6 @@ struct Number
     end
   end
 
-  # :ditto:
-  def format(separator = '.', delimiter = ',', decimal_places : Int? = nil, *, group : Int = 3, only_significant : Bool = false) : String
-    String.build do |io|
-      format(io, separator, delimiter, decimal_places, group: group, only_significant: only_significant)
-    end
-  end
-
   # Default SI prefixes ordered by magnitude.
   SI_PREFIXES = { {'q', 'r', 'y', 'z', 'a', 'f', 'p', 'n', 'µ', 'm'}, {nil, 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y', 'R', 'Q'} }