diff --git a/src/differentiate.jl b/src/differentiate.jl
index 11aa16a..04ef7dd 100644
--- a/src/differentiate.jl
+++ b/src/differentiate.jl
@@ -20,6 +20,14 @@ function differentiate(ex::Expr,wrt)
     simplify(differentiate(SymbolParameter(ex.args[1]), ex.args[2:end], wrt))
 end
 
+# a finite difference based on a symbolic expression, given a specific x to differentiate at
+function differentiate(ex::Expr, wrt::SymbolicVariable, atx::Float64)
+    ex = differentiate(ex, wrt) # symbolic only
+    local fex = :(($wrt)->($ex))
+    local f = eval(fex)
+    return f(atx)
+end      
+
 differentiate{T}(x::SymbolParameter{T}, args, wrt) = error("Derivative of function " * string(T) * " not supported")
 
 # The Power Rule: