Sticking to the plan and linking Garmin to My Fitness Plan

So with this being the first week of the Ultra training (week six in terms of the schedule) I have managed to get up at 5.30am three days in a row midweek running five miles each day, enjoyed my lie-in to 6.45am yesterday, and despite oversleeping this morning I managed to do 5.5 miles - not quite six miles but close enough.

Tomorrow I will do 15 miles and it is likely to a wet one according to weather forecast.

I have now linked the My Fitness Plan to my Garmin Connect, and now the fitness is done via Garmin, and my food record is done by My Fitness Plan - the two exchange information, so both have the knowledge and enable me to understand whether I am on track.

So far I have managed to keep my calorie consumption below my allowance each day, and there is no unhealthy snacking.

Each five mile run creates an extra 800 calories I can have on each of those days taking my allowance from 1800 to 2600 but I wonder how valid these extra calories are I.e. If I consume 2300 calories, have I really saved 300 calories or am I 500 calories over?