Trying to get some control back into my life!

Hello - new here! (Well I signed up yonks ago and did nothing with it - so new-again!)

I'm Kath, 46, mother of three, full time student. Depression, injury and a big whack of no confidence have all contributed to me gaining far too much weight which wouldn't bother me from a size/vanity perspective but is bothering me from a health point of view so it's time to do something about it. I've also signed up for the C25K programme (looking forward to W1R2 later on this afternoon), have dug out the exercise bike and am monitoring food intake. Feeling positive at the moment.

I do have a question though if anyone has any thoughts or could point me in the right direction....my exercise bike is very basic but does have a distance/timer/calorie counter on it. I'm not sure how accurate it is. When entering the exercise into the diary here it gives me different levels of activity - very light, light, moderate etc. I put 'very light' because the calories it worked out for that were nearest to my bike's measurement but I definitely worked harder today than yesterday and got hotter, sweatier and more breathless. So I would have thought that was working at a greater intensity. But I don't want to overestimate how much I've done so I wonder how you work it out? Is there a guideline somewhere?