Question on amount of calories

I started this on Jan 2, 2012. I was losing unitl February. Then it stalled and even went back up a little. After doing some looking on the internet I am convinced that I am not eating enough. I ride my stationary bike 4 times a week between 30-60 minutes each time. I had my calories at 1200 but then if I exercised it would sometimes be under 1000 calories. I don't know why I never caught that before but after looking online and finding my BMR and doing the calculations, I figured out I need 2000 calories a day. To lose weight I need to reduce this by 500 calories a day. So now MFP is set for 1500 calories. But if I exercise it will be around 1200. Will this help get the scale moving again or do I need to adjust it even more? Any suggestions? Any advice is appreciated. I

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