Roth IRA limits and cut off dates

[Matt (Semper Fi)]

Hello friends,

My wife and I recently moved our Roth IRA accounts from American Funds to Vanguard.  My money transferred first (20k), and I put it all in VTSAX.  My wife's amount is smaller, only about 6k, and it just showed up yesterday in Vanguard in a Money Market fund.  I want to jump right in and put that 6k in VTSAX, like mine, but I have a question about that.  When is the cut off to contribute to a Roth IRA for a prior year?  I know that my wife did not contribute a full 5.5k in 2016 - I believe she only contributed maybe 1.2k.  We have 20k sitting in our checking account from a bonus my wife recently got.  I would like to take a portion of that bonus, add it to the 6k from her old Roth, and have enough to get her the admiral shares in VTSAX (which is 10k minimum). 

I heard that the cut off for Roth IRA contributions for the prior year is April 1.  Is that true?  If so, would I be in compliance with the rules if I took the money sitting in my wife's Vanguard MM fund (the 6k transferred from American Funds), bought the investor shares version of VTSAX in her new Roth, immediately added 4.3k (difference between what she contributed last year, and 5.5k) before April 1 to get her the admiral shares, and then on April 2, just dump in an additional 5.5k for 2017?  Or do I even need to split it between two different days?  After the initial purchase with the 6k before April 1, could I just dump in 9.8k (total of the remainder of 2016 contributions and the full amount for 2017 contributions)?I hope this doesn't sound too garbled - I am new at this, and it's a little tough for me to put my thoughts into words.  I would appreciate any advice from the Mustache Collective!

[Khan]

When is the cut off to contribute to a Roth IRA for a prior year? 

April 15th, maybe the absolute end of tax season(April 18th this year).

Only questionably thing is whether it's April 15th hard, or before you file your taxes. Then again, googling that question immediately pops up an answer...
"Funding a Roth After Filing Taxes. You can absolutely fund a Roth IRA as long as your contribution is sent in before the official tax deadline. For this year that means all contributions made before April 15th can go toward last year's Roth IRA contribution limit."
From googling "roth ira contribution before or after tax filing"

[Matt (Semper Fi)]

Perfect!  Thank you!

[Nothlit]

For 2016, you can contribute anytime between January 1, 2016, to April 18, 2017.

For 2017, you can contribute anytime between January 1, 2017, to April 17, 2018.

In other words, you can contribute for both 2016 and 2017 today. You will have to do it as two separate transactions, but you can do them immediately one after the other.

[Nothlit]

I can't edit my post for some reason, but just wanted to say I might be wrong about having to do it as two separate transactions. It looks like Vanguard might allow you to do it as one transaction, and just specifying how much goes toward each year.