RPG Style Stat Increase

I want to make an rpg style game with different characters.
There are Stats like Health, Defence and stuff and i want to achieve that the different characters earn a different amount of stat increase on lvl up.
Since i dont want to hardcode the increase amount for every stat on each level i want to ask if theres a better way to do this.
I already thought of using curves but maybe theres an easier and more eficient way of doing this.

hardly depends what kind of bonus they should get
in the case of linear, you can just do
currentStat = baseStat + currentLevelstatBonusPerLevel
in a case of increased bonuses, you would need something like
currentStat = baseStat + baseStat * increasedStatPercent //10 str base with 20% bonus would looks like 10+10
0.2 = 12 current str

first of all thank you for the quick reply.
I want a kind of middle way.
In general the increase amount should well “increase” though i dont want a simple percent change since its kind of readable and the number becomes extremely high after some levels.
Kind of want it like its done in Mario Rpg´s so that there are good level-ups and some worse level-ups.

Curve assets are best option; combined with some small constants and small RNG.

In mario RPG, its set so that once you pass level 20, each level gives the same stat gain. To achieve that you’d only need to add a bool in your system to check if the CharLevel > X and then set the increase there. You can see how mario did it here: Super Mario RPG: Legend of the Seven Stars level up progressions - Super Mario Wiki, the Mario encyclopedia

I would definitely suggest a curve or a simple algorithm to start and then just tweak it as you go.