So I plugged in my details on the spreadsheet that the wonderful lottie sent me (thank you! ), and figured out that in order to lose 2 lbs each week I should eat about 1500-1600 calories each day. Then I sign up on sparkpeople, plug in the same data and learn that I should eat just over 1800 each day.

In between the two there's a 2lbs weight gain. Could that account for the difference in these two calorie allowances?

It's not been long since I was at about your weight. I currently eat 1700 calories daily and exercise 1 hour 5 days a week. This keeps a pretty steady loss of a lb to 1.5 lb a week. I don't know how old you are or how much exercise you're doing, but if you aren't exercising you should just try the 1600 for now. If you do a lot of exercise you might bump up to the 1800 on exercise days. Also: The easiest thing would be to pick a number, stick with that number for an entire month (stay on plan the whole month) and then see what the average loss/week is. If you're between 1 and 2 lbs, stay with what you're doing. If it's less than a lb a week, drop your calories 200 per day and try another month. If you can't stick with your calorie goal for a month because you're too hungry then up your calories a little bit and try again.

I'm not sure I understand the 2 lb weight gain part of your question, but... if I do: No, 2 lbs will not make a difference of 200 calories per day.

Every site uses different information to tell you how much you should eat. I'm pretty much the same weight as you and I can lose weight on 2000 cals a day. I walk usually 5 days a week, and lift weight 3 days (although I take a PWO shake on those days so technically I eat more those days). Everyone is completely different - the calories I eat are good for me, but not necessarily good for you (or anyone else).

sprklmajik gave the best advice when she said:

In my mind 1500-1600 calories a/day for your weight and height sounds pretty good to me. I bet your doctor would agree with that, have you talked to him/her? I totally agree with the others, what ever you do stick it out for a month or 2 and see what happens. You can either add or take away if you think the loss is too fast or too slow.