I have created a metric modulation calculator! This allows you to calculate tempos of metric modulations, including modulations using dotted notes and tuplets. Click here to download my metric modulation calculator for free (Excel or compatible program required).
The calculator relates to this former post, where I explain metric modulation.
UPDATE: There is now an online calculator that is easier than ever to use! Find the link here.
Note: if you are a web developer and would like to turn this calculator into an easy-to-use webpage (so readers can do it all from their browser), I am all ears!