diff --git a/lib/xirr/base.rb b/lib/xirr/base.rb
index 0a57c1b..596a4b4 100644
--- a/lib/xirr/base.rb
+++ b/lib/xirr/base.rb
@@ -3,7 +3,6 @@ module Xirr
   #  Base module for XIRR calculation Methods
   module Base
     extend ActiveSupport::Concern
-    require 'inline'
     attr_reader :cf
 
     # @param cf [Cashflow]
@@ -24,16 +23,8 @@ def periods_from_start(date)
     # @return [BigDecimal]
     def xnpv(rate)
       cf.inject(0) do |sum, t|
-        sum + (xnpv_c rate, t.amount, periods_from_start(t.date))
+        sum + t.amount / (1+rate.to_f) ** periods_from_start(t.date)
       end
     end
-
-    inline { |builder|
-      builder.include '<math.h>'
-      builder.c '
-        double xnpv_c(double rate, double amount, double period) {
-          return amount / pow(1 + rate, period);
-        }'
-    }
   end
 end
diff --git a/xirr.gemspec b/xirr.gemspec
index edf6c08..05e1d28 100644
--- a/xirr.gemspec
+++ b/xirr.gemspec
@@ -21,11 +21,10 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = '>=2.2.2'
 
   spec.add_dependency 'activesupport', '>= 4.1'
-  spec.add_dependency 'RubyInline', '~> 3'
 
   spec.add_development_dependency 'activesupport', '>= 4.1.0'
   spec.add_development_dependency 'minitest', '~> 5.11'
   spec.add_development_dependency 'coveralls', '~> 0'
-  spec.add_development_dependency 'bundler', '~> 1.6'
-  spec.add_development_dependency 'rake', '~> 10'
+  spec.add_development_dependency 'bundler', '~> 2'
+  spec.add_development_dependency 'rake', '~> 13'
 end