The current maximum is 3000 for Pokémon storage, and 2500 for item storage.
Originally, it was 1000.
As others have also, I fully upgraded mine.
I can also confirm that the price stayed the the same for every upgrade purchased to the maximum.
Here is a screenshot of my storage at 1000 each, and the message I got after trying to buy another upgrade once the cap was reached: Is it worth maxing Pokemon storage?
It really does come down to this: for most people, this is NOT necessary.
It simply fits the way I wanted to play Pokémon GO.
I am not interested in having the highest CP Pokémon or battling Gyms for the time being.
I simply enjoy playing "my way", I don't see the value of maxing out Pokémon Storage for 99.999% of players.
Updates:
In June 2017, max capacity for items was increased to 1500 .
In May 2018, max capacity for items was increased to 2000 .
In July 2019, max capacity for Pokemon was increased to 2500 .
In November 2019, max capacity was increased to 3000 for Pokémon and 2500 for items.
gaming.stackexchange.com/users/157272/JustAHuman
Update:
This answer is outdated.
Please refer to @JustAHuman's updated answer .
The maximum is 1000 for item storage and 1000 for Pokemon storage.
gaming.stackexchange.com/users/62235/Evorlor
EDIT:
As pointed out, the actual question is what are the maximums.
They are both 1,000.The
starting sizes are: Items: 350 Pokémon: 250
So at +50 per upgrade, the most you need to buy is: For the items: (1000-350)/50 = 13 upgrades For the Pokémon: (1000-250)/50 = 15 upgrades To see the current size, you can view via:
Select the Pokéball menu button
>
Items Select the Pokéball menu button >
Pokémon
At the top it says e.g. Items 354/350 Note that you can go over the limit - I think it is only Pokéstops
that prevent you gaining items right now but haven't checked for sure.
It might just be important events like levelling up that allow you to go over.
gaming.stackexchange.com/users/154925/Rich
The limit is 1k/1k Once you hit 1k the store informs you there is no more upgrades for each
I'm maxed on
both so this isn't random guessing
gaming.stackexchange.com/users/155168/StandandBang
You can buy upgrades in the store for your Bag and Pokémon storage until you can carry 1000 items and 1000 Pokémon.
I am at the Max on both of them, and the store does not let you purchase more upgrades.
gaming.stackexchange.com/users/155543/Hatori Sohma
In Pokemon Go, bag space and Pokemon storage are limited. First, what are the starting limits?  More importantly, there are upgrades for 50 Bag Space and 50 Pokemon. How many of each of these upgrades these can be purchased?  With all upgrades purchased, what are the resulting limits?
What are the maximum bag space and Pokemon storage? How many upgrades are needed to reach the limits?
gaming.stackexchange.com
<pokemon-go>
gaming.stackexchange.com/questions/273331
gaming.stackexchange.com/users/1410/WillfulWizard
The current maximum is 3000 for Pokémon storage. Originally it was 1000. The maximum is 3000 and 2500, however other people say it is 1000, however this may be outdated.
The maximum is 3000 according to the most upvoted user. Most users think it is 1000 however this information seems outdated.