Frontier Airlines: standard limit is 40 lb per bag — overweight or oversized bags cost extra on top of the regular baggage fee.
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41-50 lb: $50-90 extra, per bag.
Over 50 lb: often refused outright at check-in, or a steep gate fee if accepted.
Over 62 linear inches: an additional oversize fee applies.
Frontier's standard weight limit is lower than legacy carriers (40 lb, not 50) — a bag that's fine on Delta can already be overweight here.