How long after stopping Retin-A can I tan?

Tanning is only damaging your skin, You should always use an SPF when planning on having any sun exposure.  I would NOT recommend tanning!!!

If you are using Retin A properly you should have been instructed not to be exposed to excess sun.  The use of Retin A is typically done over a period of time, this results in thinning of the protective keratin layer as well as reduction of the pigment cells.  Both these facts will leave you more vulnerable to the UV radiation.  Not only you should not tan, but you should protect your skin with a complete sunblock to avoid damaging your skin permanently.  

If you stop using Retin A and your skin regains its normal color and texture then you can tolerate the tanning better.  However, this is not a good thing to do for your skin in the longrun.  

Irregardless of your Retin-A use, do yourself a favor, stop doing tanning bed! I was quoted by my published article, along with scores of other peer-reviewed articles that have demonstrated a link between skin cancers including melanoma and usage of tanning bed. See my quotes from February 9 2010 issue of BusinessWeek (http://www.businessweek.com/lifestyle/content/healthday/635508.html). With usage of Retin-A, sun sensitivity is really not an issue as long as you wear sunscreen daily as you should anyways.

If you must tan, which we would strongly suggest against, then 7 days off Retin A should be sufficient. Retin A thins the stratum corneum, which is the surface dead skin cell layer. Stopping Retin A causes a buildup of dead skin cells on the surface which offers very little but some additional protection from UV rays.
Don't tan, but if you do, go off your Retin A at least 7 days before.

Never. No dermatologist can ethically tell you that you can tan!!! Use a sunless tanning spray if you need the color but you are exposing yourself to radiation (ultraviolet) damage which will make you look much older eventually and increase your risk of skin cancer considerably! Sorry.
 

Retin-A makes you more sensitive to the sun  so you will have increased sun damage if you tan.  Tanning salons cause skin cancer as well as thin, blotchy, leathery skin.  Consider self-tanners and sunscreen instead of tanning.

If you understand all of this and still insist on tanning, stop your Retin-A 1 week before tanning and resume it immediately afterward to try and reverse some of the damage you have caused.

You shouldn't be tanning. Period. Sun exposure deactivates retin-a. I recommend SPF 50 sunscreen if you plan to be outside after using retin-a.
 

Retin-A and other topical retinoids cause desquamation or flaking of the outer layers of the epidermis.  These outer layers do provide some sun protection, so the skin of a person using retinoids is more sun-sensitive.  This flaking, however, is associated with increased skin cell turnover, providing a more youthful, glowing complexion.  Of the topicals available, retinoids are the best anti-aging products on the market.

I would suggest that if you are using retinoids to improve the appearance of your skin and reverse sun damage, you should minimize sun exposure and protect your skin from the sun with sunscreens.  The sun is the leading cause of aging changes in the skin. In addition, it increases the risk of skin cancer.

If you are using Retin A for acne, also consider that sun exposure can increase breakouts.  Although initially sun exposure may dry up existing acne, it increases oil production in the skin and leads to more breakouts later on.

Retin-A is a great way to improve the color and texture of your skin and it does so by reversing sun damage.  You might prefer to stay on the retin-a indefinitely and protect your skin from the sun- that way, your anti-aging regimen will be twice as powerful!  In fact, you might want to consider daily use of a sunblock moisturizer for your face and just cover that lighter, but healthier, skin with a darker foundation than your actual skin color.

First of all, you should not be going to the tanning bed or laying out in the sun. Tretinoin or Retin A exfoliates the skin (can help get rid of sundamaged/precancerous cells) and makes those that use it more susceptable to ultraviolet radiation damage and can increase the risk of burning. Self tanners would be recommended and continued use of the tretinion in your case.