If you haven't been together long before Christmas (less than 2 months) it is probably best to have a chat about it and set a limit with each other of something that is around 50 or under. Don't go overboard with each other because you are still in the early days and you don't know if the relationship is still going to last. If you are buying for your partners' birthday for the first time and they haven't bought for you yet, it really is up to you. As it is the first birthday and you haven't been together long, they won't be expecting much and will appreciate what you buy them (as long as there is thought in it).
If you have been together a couple of months, nearing on a year, you can spend more on each other. People tend to go wild on their first Christmases and birthdays and tone it down a bit for the following ones. Don't just spend loads of money for the sake of it; take thought into what they like as you will have a really good idea by now of what they like and don't like. If you are buying for your partners' birthday and they have already bought for you, use what they got you as a guideline. Make sure you don't out do them by spending double the amount as it may make them feel awkward and feel like they should have spent more on your present.
If the birthday is a big occasion like a 21st, 30th, etc, it would be nice to get something special. It doesn't mean you have to spend hundreds of pounds it just requires more thought. This present could include treating them to a day or evening out together, somewhere special or that they really enjoy going to, and then a present. Taking your partner somewhere for a special birthday (or any birthday) is a nice gesture and is something they can remember that you have done for them for their birthday.
Take a look at our gift ideas for men and women.