One pound in day - help explain please!

I've been on a weightloss venture for quite some tim but in april i started taking it seriously after i gained a ton of weight from school. I went from 140 to 132 (as of july 7th) but today I woke up an weighed myself after using the toilet and i gained one pound? Why? I know I didn't eat more than 3500 cals yesterday and i didn't go over board on sodium. I exercised on the bike yesterday for an hour too. I just want an explanation why this could happen. I know it seems stupid to freak out over one pound but its taken me over three months to lose 8 pounds and i don't want to gain them back. So if you have any theories on why I gained a pound please tell. Also I'm on my period right now if that affects weight gain?

You didn't really gain a pound. its water weight. probably due to TTOM. It is IMPOSSIBLE to gain 1 pound over night if you are eating in a deficit.

You shouldn't react to slight fluxuations in your weight, especially 1 pound.  I easily go up and down up to 5 pounds in a day.  The best thing to do is average your weight over a period of a week.  By doing this it will help smooth out the hills and valleys of those fluxuations.

Those fluxuations happen all the time to me and I am a guy. It must have to do with water retention and such.

Do not sweat little day to day fluctuations like that.

You can drive yourself crazy if you look at weight gains/losses day to day.  Even so, I still hit the scale every morning, and fluctuations of even a couple pounds here and there are common due to water weight.  I keep my eye on the green trend line and trend weight on the weight log, as long as that continues to go down I am a happy man!

First of all, CONGRATS on losing 8lbs the healthy way :)

And secondly, theres no way you could have gained a pound like that and you know it so don't worry about it. Just keep eating healthy and watching your calories. I know its hard to leave the scale alone but try checking the scale only once or twice a week. This will ease your mind and keep you from worrying over small ups and downs that are bound to take place.

Good luck and congrats again!

It's because it's that time of the month. This is VERY common with women. Don't sweat it. Keep up your exercise routine as well as counting/controlling daily caloric intake. You should see a difference once "Aunt Betty" leaves the scene. (Aunt Betty was an aunt we hated as kids so my sis and I named our period after her)

Don't panic! I also feel extra fat and bloated when it's that time of the month.  And I am usually 2 or so pounds heavier at night than in the morning.  Which is why I weigh only in the morning when I get up, after I go to the toilet. :o)

It's just water weight. My weight can fluctuate by a few pounds either direction due to water. Just drink lots of water for a day or two and it will go away. Definitely don't stress yourself over it.