Adding a line on T-Mobile's new T-Mix plans costs $30 to $65 a month for the second line, depending on the plan, and $15 to $40 for a third or fourth. On T-Mix Standard, for example, two lines are $85 a month and three are $100. You can add a line in the T-Life app, online or in a store, and T-Mobile charges a one-time connection fee per line.
What adding a line costs on T-Mix
| Plan | 1 line | Add a 2nd line | Add a 3rd line | Add a 4th line |
|---|---|---|---|---|
| T-Mix Standard | $55 | +$30 ($85 total) | +$15 ($100) | +$15 ($115) |
| T-Mix More | $75 | +$55 ($130) | +$25 ($155) | +$25 ($180) |
| T-Mix Loaded | $95 | +$65 ($160) | +$40 ($200) | +$40 ($240) |
The second line is the expensive one; the third and fourth cost much less. Each line also adds Picks, T-Mobile's choose-your-perk credits: up to 4 on Standard, 7 on More and 11 on Loaded with four lines. See our T-Mix breakdown for what each plan includes.
A worked example
| T-Mix Standard | T-Mix More | T-Mix Loaded | |
|---|---|---|---|
| 3 lines, per month | $100 | $155 | $200 |
| 4 lines, per month | $115 | $180 | $240 |
| Cost of the 4th line, per year | +$180 | +$300 | +$480 |
One-time fees and extras
- A one-time connection charge, $35 per line, on new lines. T-Mobile sometimes waives it online, so check at checkout.
- A financed phone adds its own monthly payment.
- Smartwatches, tablets and hotspots go on connected-device plans, billed separately from phone lines.
- Device protection is charged per phone.
How to add a line
- Open the T-Life app (or sign in at t-mobile.com) as the account holder.
- Choose to add a line, and pick a new number or bring one from another carrier.
- Pick a phone, or bring your own unlocked phone.
- Use an eSIM to start right away, or wait for the SIM card.
- If you're bringing a number, have the other carrier's account number and transfer PIN ready.
On an older T-Mobile plan?
Experience and Essentials plans have their own per-line prices, and T-Mobile runs third-line promos that change. Check the add-a-line price in T-Life before you commit, and read is T-Mix worth it before switching plans just to add a line.
Ways to pay less for the new line
- Add the line during a new-line promo; new lines often get phone deals upgrades don't.
- Bring your own phone to skip the device payment.
- Pick the T-Mix plan by what the whole account needs; you can't save by putting one person on a cheaper tier if the plan is shared.
- If the person doesn't need T-Mobile's perks, a separate prepaid line on T-Mobile's network costs less.
On a 12-month plan, paid upfront, taxes and fees extra. A cheaper second line on the same towers if it doesn't need T-Mobile's perks.
See Mint plans →Prices checked October 31, 2026. We may earn a commission if you sign up through this link, at no extra cost to you.
Common problems
| Problem | Fix |
|---|---|
| The add-a-line option isn't there | Only the account holder (or someone with full permissions) can add lines. |
| Credit check limits your lines or asks for a deposit | T-Mobile can cap lines by credit; paying the phone in full or bringing your own can help. |
| Bringing a number fails | Check the other carrier's account number, transfer PIN and billing ZIP. See [how long a port takes](BlogPost%20News%201a.dc.html?post=how-long-to-port-a-number). |
| First bill looks high | It can include a partial month for the new line plus the connection charge. |
Frequently asked questions
How much is it to add a line on T-Mobile? +
Can I add a line on T-Mobile online? +
Does adding a line on T-Mobile need a credit check? +
Can I bring my own phone to a new T-Mobile line? +
Is the second or third line cheaper on T-Mobile? +
Do new T-Mobile lines get Picks? +
Can I add a watch or tablet to T-Mobile? +
Is it cheaper to add a T-Mobile line or get Mint? +
Keep reading
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Jean has tested carrier plans independently since 2019, running SIMs on all three networks and paying for every line himself. He ranks carriers on the bill you actually get, taxes and fees included, not the price on the ad.