Best inexpensive Heart Rate Monitor for tracking calories bu

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Hi, I have recently started increasing my exercise, I go swimming, do a dance class, do the 30ds and a Pilates class as well as jogging at the weekend. I also have a mini cross trainer at home that I go on. I currently exercise every day and for at least 30 minutes, most days 50 mins to 1 hour of some description.

I know the exercise calories burned on MFP are not that accurate. Can anyone recommend a good heart rate monitor that is not too expensive that would show more accurately the number of calories burned?

I know I might not get a cheap one that I can use in the water but I am new to this field and wondered if I needed one with a chest strap or if I could get a strapless one.

I dont need anything all singing all dancing, just something that measures the calories burned more accurately.

Can anyone recommend one to me? I am from the UK, have access to the internet and have incredibly small wrists- as in I have to buy childrens watches. I just wish the rest of me matched my wrists!!!

Thanks for your help,

Emma.