Confused!

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Hi,
I have just finished tracking my food fo the day - I have stayed within my alowance of 1300 calories. I am 129lb and when I finished - it said "If you continue like this you will weigh 128.6lb in five weeks" Since I have been on 1300 calories since May last year and lost 40lbs, I don't understand why I will only lose 1/2 lb in five weeks. Should I be putting my calorie allowance right down now?