4% is a good start! Good for you.
Does your company offer a matching contribution? If so, make sure you’re saving enough to get the maximum. Many companies will match some or all of the first 6% you save, so you might want to increase another 2% sooner.

A good rule I’ve read is to increase how much you save by 2% each year, usually when you get an annual raise (some for yourself now, and some for yourself later in retirement)