Will refinancing save me money?

I have been getting letters from places telling me I should refinance now and save money since the interest rates are low. I am trying to figure out whether the options for mortgage refinancing London companies are offering me will really save me money after all is said and done. Is there a good way to figure this out? There must be calculators somewhere that could help me figure this out, and I would really love to find out where they are so that I can crunch some numbers without having to try to figure out formulas since I am not that great at math.