Estimate before loading
Multiply expected paid journey groups by the relevant base fare, then add a distance allowance if many trips exceed 10 km. Do not count every tap as a new base fare when a valid transfer applies. The calculator uses this approach and shows the assumption.
Use staged loading
Load enough for the first two or three days, check the balance, then add more. This reduces the chance of a large leftover balance and makes an imperfect estimate easy to correct. A separate retail payment balance on another product does not automatically top up ordinary T-money.
Refunds are a fallback
VISITKOREA says smaller T-money balances can be refunded at convenience stores while larger refunds have a more restricted process. Exact fees and locations can change, so efficient staged loading is simpler than planning around a refund.