Why your monthly bill hides the real price
Marcus pays 85 a month for a single line on a big-carrier unlimited plan. His coworker pays25 a month on a prepaid plan with 15 GB and uses Wi-Fi most of the day. Same phone, same city, same coverage. The difference is $720 a year. Marcus never compared because the sticker price felt normal, and the real cost was buried in autopay.
The number carriers don't advertise is your cost per gigabyte. A $70 unlimited plan sounds generous, but if you actually use 8 GB a month, you are paying roughly 8.75 per GB for data you never touch. A30 plan with 10 GB costs $3 per GB. Two of those, and you are paying for headroom you will never fill. This calculator surfaces that number directly so the comparison stops being about the headline price.
Cost per line is the second hidden lever. A family plan advertised at $140 for four lines is $35 per line, which can beat a $45 single line. But add a fifth line at $50 and the average climbs. Enter each plan's total and its number of lines, and the tool divides it out so you are comparing apples to apples instead of guessing whether "unlimited for the family" is actually a deal.
The U.S. wireless market is competitive, and prepaid and mobile virtual network operators (carriers that lease the same towers) often run the same coverage at half the price. The reason most people overpay is not bad math, it is no math. They never sat down and laid four plans next to each other. Enter your candidates, your line count, and your real data usage, and the annual total tells you which plan wins over twelve months, not just this month.
Quick question: do you know how many gigabytes you actually used last month? Most people guess high. Check your phone's data usage screen, enter the real figure, and the cost per GB column often reveals you are paying premium rates for an unlimited plan you treat like a 6 GB one.