What is the cutoff date to convert 403B to Roth 403B?

[aceyou]

Just had a thought pop into my mind...

I sheltered a TON this year through 403's and 457's, so I'll hardly pay any federal or state taxes.  Maybe I should:

a) open up a Roth 403B at my workplace (I have access to one)
b) transfer some money from my 403B to the Roth 403B. 

This might be hard to pull off before the new year.  Anyone know if December 31 the cutoff date to do this, or could I do it by April 15 and tag it for the 2016 fiscal year (I don't know if this is a thing or if I just made it up)? 

[MDM]

Anyone know if December 31 the cutoff date to do this

Yes, it is.

Conversions are taxable in the calendar year they are made.  They cannot be recharacterized as an IRA can.  See The 411 On Roth 401(k) Conversions | Bankrate.com for more.

[aceyou]

Thank you so much.