Calculate overage fees for going over data limits.
An overage bill has two components people forget. The first is the excess itself, which is usage minus allowance and never negative. The second is block rounding: most carriers bill overage in fixed increments — often 1 GB, sometimes far larger — and round every part-block up, so going 200 MB over a 50 GB plan can cost the same as going a full gigabyte over. Comparing the resulting charge against the price difference to the next tier up is usually decisive, because overage rates are typically five to twenty times the marginal cost of included data, which is exactly why they exist.
Metered overage charge
Excess = max(0, used - included); blocks billed = ceiling(excess / block size); charge = blocks billed x block size x rate per GB
Almost always, if you exceed the allowance regularly. Compare this charge with the monthly price gap to the next tier — if the overage is larger even once a quarter, the upgrade usually wins.
Block rounding. If overage is billed per gigabyte, 1 MB and 999 MB of excess cost the same, which is what the paid-for-but-not-used figure here exposes.
Many do, especially on unlimited plans with a fair-use threshold. In that case set the rate to zero and read the excess figure as the amount of data delivered at reduced speed rather than a bill.