Why does my wallet size increase over time?

[Geremia]

Why does the size of the output of

bitcoin-cli backupwallet

or, equivalently, wallet.dat

increase over time?

(cf. the related Bitcoin StackExchange question.)

[Enzyme]

I'm not too sure but I think change addresses are created every 100 transactions, therefore accounting for the increase in size.

[Newar]

A good number of things in there that grow bigger as you use the software: https://en.bitcoin.it/wiki/Wallet

[achow101]

As you use more than 100 hundred addresses, Bitcoin Core will generate another 100 address for the keypool. Generating and storing those 100 new keys will of course take up some extra space. If you are doing Bitcoin transactions with the principle one input one output, then you will have to generate 100 new addresses after 100 transactions.

[shorena]

As you use more than 100 hundred addresses, Bitcoin Core will generate another 100 address for the keypool. Generating and storing those 100 new keys will of course take up some extra space. If you are doing Bitcoin transactions with the principle one input one output, then you will have to generate 100 new addresses after 100 transactions.

Private keys for the keypool are not created in patches of 100, they are created whenever possible (wallet is unlocked) to match the requested (either per default or config) keypool size. IIRC getwalletinfo shows how many unused keys are currently available. You will notice that this number is almost never below 100 unless you spam the "New" button.