diff --git a/init.sh b/init.sh
index 65235f0..8e6b906 100755
--- a/init.sh
+++ b/init.sh
@@ -1,4 +1,4 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source "$CURRENT_DIR/scripts/helpers.sh"
diff --git a/net_speed.tmux b/net_speed.tmux
index a81f908..07691bf 100755
--- a/net_speed.tmux
+++ b/net_speed.tmux
@@ -1,4 +1,4 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source "$CURRENT_DIR/scripts/helpers.sh"
@@ -13,7 +13,7 @@ upload_interpolation="\#{upload_speed}"
 
 do_interpolation() {
 	local input=$1
-    local result=""
+	local result=""
 
 	result=${input/$download_interpolation/$download_speed}
 	result=${result/$net_interpolation/$net_speed}
diff --git a/run-tests.sh b/run-tests.sh
index 70f0d41..7ed1757 100755
--- a/run-tests.sh
+++ b/run-tests.sh
@@ -1,4 +1,4 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 CURRENT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 for testSuite in $CURRENT_DIR/tests/suites/* ; do
diff --git a/scripts/download_speed.sh b/scripts/download_speed.sh
index 66f5511..493b77e 100755
--- a/scripts/download_speed.sh
+++ b/scripts/download_speed.sh
@@ -1,28 +1,15 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source "$CURRENT_DIR/helpers.sh"
 
-sum_download_speed()
-{
-    # Output uses first column
-    sum_speed 1
-}
-
 main()
 {
-    # TODO make configurable
-    #local file=$(get_tmux_option $DOWNLOAD_FILE)
-    local file=$DOWNLOAD_FILE
-    local old_val=$(read_file $file)
-    local new_val=$(sum_download_speed)
-
-    write_file $file $new_val
-    local vel=$(get_velocity $new_val $old_val)
+    local speed=$(get_speed 1)
 
     ## Format output
     local format=$(get_tmux_option @download_speed_format "%s")
-    printf "$format" "$vel"
+    printf "$format" "$speed"
 }
 main
 
diff --git a/scripts/helpers.sh b/scripts/helpers.sh
index 6877eac..aa7b3ca 100644
--- a/scripts/helpers.sh
+++ b/scripts/helpers.sh
@@ -1,10 +1,11 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 ##
 # Varialbes
 ##
-DOWNLOAD_FILE="/tmp/tmux_net_speed.download"
-UPLOAD_FILE="/tmp/tmux_net_speed.upload"
+LAST_FILE="/tmp/tmux_net_speed.last"
+_last=()
+_current=()
 
 get_tmux_option() {
     local option=$1
@@ -28,12 +29,12 @@ get_velocity()
 {
     local new_value=$1
     local old_value=$2
+    local interval=${3:-$(get_tmux_option 'status-interval' 5)}
 
     # Consts
     local THOUSAND=1024
     local MILLION=1048576
 
-    local interval=$(get_tmux_option 'status-interval' 5)
     local vel=$(( ( new_value - old_value ) / interval ))
     local vel_kb=$(( vel / THOUSAND ))
     local vel_mb=$(( vel / MILLION ))
@@ -87,12 +88,22 @@ write_file()
 
 get_interfaces()
 {
+    local os=${1:-$(os_type)}
     local interfaces=$(get_tmux_option @net_speed_interfaces "")
 
     if [[ -z "$interfaces" ]] ; then
-        for interface in /sys/class/net/*; do
-            interfaces+=$(echo $(basename $interface) " ");
-        done
+        case $os in
+	    freebsd|osx)
+		for interface in $(ifconfig -l); do
+		    interfaces+="$interface "
+		done
+		;;
+	    linux)
+        	for interface in /sys/class/net/*; do
+            	    interfaces+=$(echo $(basename $interface) " ");
+        	done
+		;;
+	esac
     fi
 
     # Do not quote the variable. This way will handle trailing whitespace
@@ -101,19 +112,61 @@ get_interfaces()
 
 sum_speed()
 {
-    local column=$1
+    local os=$(os_type)
+    local down_total=0
+    local up_total=0
 
-    declare -a interfaces=$(get_interfaces)
+    declare -a interfaces=$(get_interfaces $os)
 
-    local line=""
-    local val=0
     for intf in ${interfaces[@]} ; do
-        line=$(cat /proc/net/dev | grep "$intf" | cut -d':' -f 2)
-        speed="$(echo -n $line | cut -d' ' -f $column)"
-        let val+=${speed:=0}
+	case $os in
+	    freebsd|osx)
+		line=( $(netstat -I "$intf" -ibn | grep 'Link#' | awk '{ print $(NF-4), $(NF-1) }') )
+		;;
+	    linux)
+		line=( $(cat /proc/net/dev | grep "$intf" | cut -d':' -f 2 | awk '{ print $1, $9 }') )
+		;;
+	    esac
+	let down_total+=${line[0]}
+	let up_total+=${line[1]}
     done
 
-    echo $val
+    echo $down_total $up_total
+}
+
+# 1 - download, 2 - upload
+get_speed()
+{
+    local column=$1
+    local subprocess=${2:-0}
+    local interval=$(get_tmux_option 'status-interval' 5)
+    local now=$(date +%s)
+
+    # timestamp download_cumulative upload_cumulative
+    local last=( "${_last[@]}" )
+    if [ ${#last[@]} -eq 0 ]; then
+	last=( $(read_file "$LAST_FILE" "$now 0 0") )
+	_last=( "${last[@]}" )
+    fi
+    # protect against division by 0
+    if [[ $last -eq $now ]]; then sleep 1; now=$(date +%s); fi
+    local current=( "${_current[@]}" )
+    if [ ${#current[@]} -eq 0 ]; then
+	current=( $now $(sum_speed) )
+	_current=( "${current[@]}" )
+    fi
+    local delta_t=$(( $current - $last ))
+    local speed=$(get_velocity ${current[$column]} ${last[$column]} $delta_t)
+
+    if [[ $subprocess -eq 0 ]] && [[ $((${last[0]}+$interval)) -le $now ]]; then
+	function update_last()
+	{
+	    write_file "$LAST_FILE" "${_current[*]}"
+	}
+	trap update_last EXIT
+    fi
+
+    echo $speed
 }
 
 is_osx() {
@@ -128,3 +181,25 @@ command_exists() {
     local command="$1"
     type "$command" >/dev/null 2>&1
 }
+
+os_type() {
+    local os_name="unknown"
+
+    case $(uname | tr '[:upper:]' '[:lower:]') in
+      linux*)
+        os_name="linux"
+        ;;
+      darwin*)
+        os_name="osx"
+        ;;
+      msys*)
+        os_name="windows"
+        ;;
+      freebsd*)
+        os_name="freebsd"
+        ;;
+    esac
+  
+    echo -n $os_name
+}
+
diff --git a/scripts/net_speed.sh b/scripts/net_speed.sh
index 5390925..b4ca7ea 100755
--- a/scripts/net_speed.sh
+++ b/scripts/net_speed.sh
@@ -1,12 +1,14 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source "$CURRENT_DIR/helpers.sh"
 
 main()
 {
-    local download=$("$CURRENT_DIR/download_speed.sh")
-    local upload=$("$CURRENT_DIR/upload_speed.sh")
+    # calls within $() are in subprocess shells, run first to cache values
+    get_speed 1 >/dev/null
+    local download=$(get_speed 1 1)
+    local upload=$(get_speed 2 1)
 
     ## Format output
     local format=$(get_tmux_option @net_speed_format "D:%10s U:%10s")
diff --git a/scripts/upload_speed.sh b/scripts/upload_speed.sh
index b66477b..a76341a 100755
--- a/scripts/upload_speed.sh
+++ b/scripts/upload_speed.sh
@@ -1,28 +1,15 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source "$CURRENT_DIR/helpers.sh"
 
-sum_upload_speed()
-{
-    # Output uses ninth column
-    sum_speed 9
-}
-
 main()
 {
-    # TODO make configurable
-    #local upload_file=$(get_tmux_option $UPLOAD_FILE)
-    local file=$UPLOAD_FILE
-    local old_val=$(read_file $file)
-    local new_val=$(sum_upload_speed)
-
-    write_file $file $new_val
-    local vel=$(get_velocity $new_val $old_val)
+    local speed=$(get_speed 2)
 
     ## Format output
     local format=$(get_tmux_option @upload_speed_format "%s")
-    printf "$format" "$vel"
+    printf "$format" "$speed"
 }
 main
 
diff --git a/tests/suites/helpers.test.sh b/tests/suites/helpers.test.sh
index a68bbb1..8062305 100755
--- a/tests/suites/helpers.test.sh
+++ b/tests/suites/helpers.test.sh
@@ -1,4 +1,4 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 
 CURRENT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 SCRIPTS="$CURRENT_DIR/../../scripts"
diff --git a/tests/test_utils.sh b/tests/test_utils.sh
index 045d3e5..934767f 100644
--- a/tests/test_utils.sh
+++ b/tests/test_utils.sh
@@ -1,4 +1,4 @@
-#!/bin/bash -
+#!/usr/bin/env bash
 ###############################################################################
 # Author: Travis Goldie
 # Purpose: Util funcs for unit tests