Can you post a picture? They symptoms of over and under watering can be similar, plus there are other things that can make leaf edges turn brown too (low humidity, salt/fertilizer buildup in the soil, etc). To check on your watering, wait until the next time you were planning to water, but before you do, stick your finger down a couple inches into the pot and see how wet it feels. If it's bone dry then you probably need to water more often, but if it's sopping wet then you're watering too much. If it's neither of those then your watering is probably OK and it's something else causing the browning edges.
Is your banana indoors? Probably so this time of year... It could be the lack of humidity in the house. With the heater on etc. the air is drier inside. You might want to try misting the leaves a little a few times per day.