Updated

If you're one of the 200 million wireless customers of AT&T or Verizon, it's time to make a decision about shared data plans.

Verizon rolled out its Share Everything plans to new customers back in June. The mobile operator allows current customers to stay on tiered plans if they prefer. Those on grandfathered unlimited plans must switch to a tiered plan or a Share Everything plan to get a subsidized phone.

AT&T's Mobile Share launches Aug. 23. The carrier has said it will continue to offer traditional plans to new and current customers. Those with grandfathered unlimited plans can keep them.

Even if you're happy with your tiered or grandfathered unlimited plan, it pays to learn the ins and outs of these new shared data plans. A shared plan might save your family money and offer more features than you're getting now.

Shared plans from AT&T and Verizon start out by giving users unlimited talk and text. Your monthly wireless bill is determined by how many gadgets you want covered and how much data you want to share among them.

Up to 10 devices can be used on a plan. You can cover smartphones, feature phones, tablets and laptops/connect cards/netbooks. AT&T and Verizon charge a monthly base fee of $30 for a feature phone, $10 for a tablet and $20 for a laptop/connect card/netbook. (There is no extra charge for tethering - that's using a smartphone or tablet to share an Internet connection with other devices.)

At Verizon, each smartphone costs $40 per month. A smartphone costs $45 on AT&T's 1GB plan, $40 on the 4GB plan, $35 on the 6GB plan and $30 on the 10-20GB plans.

Shared data plans let family members draw from a monthly pool of data. You don’t have to buy a data plan for Mom, a data plan for Dad and a data plan for Junior.

The good news for light data users is that AT&T and Verizon shared plans start at 1GB. Verizon's 1GB is $50, while AT&T's is $40. From there, AT&T jumps to a $70/4GB level.

The 4GB Verizon plan also costs $70. A family using 4GB of data with 2 smartphones, one basic phone and one tablet would pay $190 per month at Verizon and AT&T.

Unlike AT&T, Verizon offers a 2GB/$60 data plan. That could be the sweet spot for many families.

AT&T's higher allotments include 6GB/$90, 10GB/$120, 15GB/$160 and 20GB/$200.
Verizon's data levels step up in 2GB/$10-a-month increments, maxing out at 20GB/$150.

Generally, shared data plans are a good fit for families that still talk and text a lot, like to use cellular-capable tablets and don't burn up excessive amounts of data. Singles who are heavy data users might want to consider sticking with a traditional plan, switching to prepaid or switching to an unlimited data plan at Sprint or T-Mobile.

Everyone's needs are different. That's why I made this handy calculator to help you decide which shared data plan is best for you. Just enter the number of devices you have and it tells you the monthly cost for each data plan on both carriers.

Before you choose a level, it's essential that you have an accurate picture of how much data your family uses per month. Log in to your online account and examine your usage over the past six months and then use that as your guide.

That is, unless you've made a major change recently or are planning to. For instance, have you recently upgraded to faster 4G LTE smartphones and/or tablets recently, or do you plan to now? If so, you are likely to consume more data in the future than your six-month check will indicate.

Verizon and AT&T both have usage calculators on their websites that will help you visualize how much data it takes to stream video and accomplish other Internet tasks that may be relatively new activities for you.

Finally, don't guess too low. Verizon and AT&T will charge you $15/GB for going over your allowance. That can blow up the monthly family budget pretty quickly!

Kim Komando hosts the nation's largest talk radio show about consumer electronics, computers and the Internet. Get the podcast or find the station nearest you at www.komando.com/listen. Subscribe to Kim's free e-mail newsletters at www.komando.com/newsletters. Copyright 1995-2012, WestStar TalkRadio Network. All rights reserved.