Can I monitor traffic through router to ISP

I am on a 20 GB a month broadband limit. My ISP (BT) has a usage monitor page which tells me how much of the 20 GB I have used so far this month (16.49 GB to midnight yesterday) but my average is only 13 GB per month. I have a usage monitor on my computer but how do I measure the amount of usage which is passing through my router (BT Home Hub 5) including tablets and phones which are connected by WiFi?
I rang BT today and they told me that I had used 4 GB in one 24 period this month plus 2 GB and 1.5 GB on other days. The two latter amounts can probably be explained by my granddaughter playing Minecraft on an iPad but I am completely at a loss to explain the 4 GB because she didn't arrive until after school that day.
I am satisfied my router is secure and not being accessed by anyone outside the house.
Mike

Edited by deleted (Sun 22-Feb-15 21:19:24)

You'd need a router that has the capability to measure total throughput and not lose the data in the event of power cycling.

If you are getting close to the 20GB regularly why not pay the extra for unlimited.

Thank you for your response. I don't normally get close to the 20 GB limit so in the first instance I am trying to establish what is causing the problem before I start spending more money.

In reply to a post by MJHulme:

but I am completely at a loss to explain the 4 GB because she didn't arrive until after school that day.

You need to get your granddaughter to leave her iPad at home!

For a couple of months, we had to resort to EE 4G while our broadband connection was provisioned, and some usage effects seemed strange. I had already re-flashed the router so it would work with a 4G modem - so just added some monitoring rules to the (Linux-based) firewall on the router.

It was frightening how fast my daughter could go through bandwidth on her iPad. Without ever really noticing, and in just the period after getting home from school. She could outpace my wife's usage - and she'd be connected to work's VPN all day long.

Not forgetting the day that my PC decided to download a new map for the Garmin while all the humans were watching TV. That was more than 4GB ...

DSLstats has a traffic monitor setting and seems good on my modem.

http://www.s446074245.websitehome.co.uk/trafficconfi...

Thank you for your thoughts but I don't really want to stop her bringing her iPad - I might instantly lose all the good granddad points I have accumulated over the years!

Hello Aptman - I have downloaded the DSLstats software but I just can't work out what to put in all the boxes. Unfortunately my BT Hub 5 does not appear in the drop down list of pre-defined entries. Has anyone used this software with a BT Hub 5 and worked out what details the software wants. I do of course have all the hub numbers that are printed on the removable plastic card and I know how to log into it through my web browser.
Help setting up the DSLstats software would be appreciated.

It doesn't work with the HH5.

Thank you for that. No wonder I was struggling.