help with calories intake calculation?

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I'm having trouble calculating how many calories I need a day in order to lose 1/2 - 1 lb a week.
I'm 5'3, 25 years old, cw is 137. I am doing p90x 6 days a week and I walk 4 miles 2-3 a week.

Can anyone help me to calculate this please?

Thanks in advance

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