Your 50 nights remain in your lifetime balance and you have the opportunity to attain platinum by adding 25 additional nights by 12/31/14 (75 nights needed for platinum). If you do not achieve platinum any nights you add this year between 50-75 will rollover to start your 2015 measurement period (status for 2016). So if you stay a total of 60 nights for 2014 you will have Gold status and start 2015 measurement period with a carryover balance of 10 nights. There are many threads on this topic that can provide more details and do a better job of explaining than I have. Congratulations on achieving Gold status.
Hii there, Debs, and welcome to our community. Congrats on the Gold status.
When you register with Rewards Marriott will keep a count on the number of nights you stay in any calendar year. Once you've stayed 10 nights you'll be awarded silver status (lots of words, but in reality only 2 benefits of any value, the extra 20% points and a higher prospect of getting a late checkout).
Once you stay 50 nights you are awarded Gold status, which I think everyone who stays regularly at the full service hotels agrees is where the meat of Marriott Rewards is to be found, room upgrades, free breakfast 7 days week, free in-room wifi and lounge access. Theres also the extra points, but that's not worth much (extra half point per $!)
FInally there's Platinum, awarded if you stay 75 nights in a calendar year, which has all the benefits of silver and gold plus 500 extra points at checkin, 25% extra points and 48-hour availability. Whilst a nice bump from Gold, it's not worth making an especially big effort to attain. There's also a level called "Platinum Premier" which apparently is awarded to the top 3% of Plats, although how that 3% is measured is a secret... In any event according to those who have it, it's a pretty empty vessel benefits-wise and carries no extra points over Plat.
Now the year hasn't yet finished so I assume you're going to stay a few more nights, maybe another 10, which will mean you've stayed 60 nights in 2014. At the beginning of January 2015 the nights counter that so proudly shows 60 will reset back to zero, but any nights over the 50 for gold will be carried forward, called a rollover. So about halfway through January you'll find these credited to your account meaning you'll only have to stay 40 more nights to get to Gold, or 65 to get to Plat, whatever status you reach during 2015 will be awarded to Feb 2017.
If your counter shows less than 50 nights at the end of 2016, inc rollovers, Credit card nights, meetings and bonuses (make sure Marriott knows your DOB and you'll get 1 bonus night credit on your birthday), you'll have failed to requalify and your Gold status will run out in February 2017 when you'll be relegated to Silver.
Hope this helps