T-Mobile's line addition fee and monthly cost

Adding a line to your T-Mobile account costs nothing upfront, but you will pay a monthly charge for the new line itself. The monthly cost depends on which plan you have: if you are on a T-Mobile Magenta plan, each additional line runs $25 per month. If you are on Magenta Max, each additional line is $55 per month. These prices assume you bring your own phone or buy one outright — if you finance a phone through T-Mobile, you add the device payment on top of the line cost.

T-Mobile does not charge a separate set up fee to add a line, though some third-party retailers (Best Buy, Costco, or local phone shops) may charge their own setup fees. If you add the line directly through T-Mobile's website, app, or a company-owned store, there is no set up fee.

The monthly charge starts the day the line is activated. You will not be charged for a partial month — if you add a line on the 15th, you pay the full monthly rate starting that day, and your next billing cycle includes the full charge.

Key Takeaways

  • T-Mobile charges $25 per month for each additional line on Magenta plans and $55 per month on Magenta Max plans, with no upfront set up fee.
  • The monthly line charge begins the day you set up the line and appears on your next bill, not prorated by the day.
  • If you finance a phone through T-Mobile at the same time, the device payment is separate from and added to the line cost.
  • Adding a line through T-Mobile's website, app, or company store avoids third-party retailer fees that some locations charge.

How to add a line without visiting a store

You can add a line to your T-Mobile account online through the T-Mobile website or the T-Mobile app without going to a physical location. Log into your account, select "Add a line," and follow the prompts. You will need to choose whether you are bringing an existing phone, buying a new one, or financing one through T-Mobile. If you already have a phone to use, the process takes about five minutes and the line activates within hours.

If you are buying a new phone, you can order it at the same time and T-Mobile will ship it to you. The line itself activates right away, but you will need the phone to arrive before you can use the line on a device. If you are financing a phone, T-Mobile runs a credit check and you will see the monthly device payment added to your bill alongside the line cost.

You can also call T-Mobile customer service at 611 from any T-Mobile phone, or 1-844-839-4534 from any phone, and a representative will add the line for you over the phone. This route takes longer but may be easier if you have questions about which plan option fits your needs.

What happens if you bring your own phone

If you already own a phone and want to use it on the new line, you only pay the monthly line cost — nothing extra. T-Mobile will ask you for the phone's IMEI number (a unique identifier for the device) to make sure it is compatible with their network. You can find the IMEI by dialing *#06# on the phone, or by looking in the phone's settings under "About Phone."

The phone must be either unlocked or previously activated on T-Mobile. If the phone is locked to another carrier, you will need to contact that carrier and request an unlock before T-Mobile can set up it. Once the line is active, you can move your old phone number to the new line, or T-Mobile will assign a new number — you choose during setup.

Financing a phone on the new line

If you want to buy a new phone when you add the line, T-Mobile offers two payment options: pay the full price upfront, or finance it over 24 months with no interest. The monthly device payment appears separately on your bill from the line cost. For example, if you add a line on Magenta ($25/month) and finance a $600 phone, your bill shows $25 for the line plus roughly $25 per month for the phone, totaling $50 monthly.

T-Mobile runs a credit check before approving financing. If you do not meet their credit requirements, you can still add the line and buy the phone at full price instead. Some phones also may have access to for T-Mobile's trade-in program, where you trade in an old phone and receive a credit toward the new one, lowering the amount you finance.

Family plans and discounts on multiple lines

T-Mobile's Magenta plan is designed for multiple lines — the first line costs $65 per month, and each additional line costs $25. If you add four lines total, you pay $65 + $25 + $25 + $25 = $140 per month. Magenta Max works the same way: the first line is $85 per month, and each additional line is $55, so four lines cost $85 + $55 + $55 + $55 = $250 per month.

T-Mobile occasionally runs promotions where the cost of adding a line is reduced or waived for a limited time, though these are not may provide. If you are a military member, first responder, or student, T-Mobile offers discounts on the monthly bill that explore to all lines on the account. Check the T-Mobile website or ask in-store whether you may have access to for any of these discounts before adding a line.

What to expect on your first bill after adding a line

Your bill will show the new line as a separate item with its own phone number. The line charge appears on the bill for the month it was activated, even if you activated it partway through the billing cycle. If you activated the line on the 20th of the month and your billing cycle ends on the 30th, you still pay the full monthly line cost on that bill.

If you financed a phone, the device payment also appears on the same bill. Some people are surprised by the total because they expected a prorated charge — T-Mobile does not prorate line costs. If you want to avoid a large first bill, you can add the line near the start of your billing cycle so the charges spread across fewer days before the next full month begins.

Removing a line if you change your mind

You can remove a line from your account at any time through the T-Mobile app, website, or by calling customer service. There is no fee to remove a line. If you financed a phone on that line, you still owe the remaining balance on the device payment — removing the line does not cancel the phone payment.

Once you remove a line, the phone number is released and may be reassigned to another customer after a waiting period. If you think you might want that number back, contact T-Mobile before removing the line to see if they can preserve it temporarily.

Frequently Asked Questions

Can I add a line if I am not the account holder?

No. Only the account holder or someone with authorized account access can add a line. If you are not the account holder, ask the person who is to add the line for you, or contact T-Mobile to request authorization to manage the account yourself.

Do I need a new phone number when I add a line?

You can choose. T-Mobile will assign a new number automatically, but during setup you can request to port in a number from another carrier if you have one. If you want to keep an existing T-Mobile number on the new line, that is also an option — you would move the number from another device on your account.

What if I add a line but do not use it for a while?

You will still be charged the monthly line cost even if the line sits unused. T-Mobile does not have a grace period or pause option for individual lines. If you do not plan to use the line, remove it from your account to stop the charges.

Can I add a line to a prepaid T-Mobile account?

No. T-Mobile's prepaid service (T-Mobile Prepaid) does not support multiple lines on one account. Each prepaid line is separate. If you want multiple lines under one account, you need to switch to a postpaid plan like Magenta or Magenta Max.

Does adding a line affect my current plan or pricing?

No. Your existing plan and pricing stay the same. The new line is added at the standard rate for your plan, and you do not get a discount on your existing line. Your total bill increases by the cost of the new line only.