Update July 2021
The NNS team just released an update that makes this process significantly easier. Click on a neuron and click “Increase Neuron Stake”. Then choose the account from which you would like to transfer your ICP, and submit it. And that’s all! Everything below this is how you would do it before this NNS update.
This is one of the most frequent questions I have received because once you stake your ICP, it is inevitable that you will buy more and want to stake it in the same neuron. Here is how to add ICP to a staked neuron: 1. Find the wallet address of your staked neuron You can find the wallet address of your staked neuron by looking at the transaction history of your Main wallet in the NNS (or whichever wallet you used to stake ICP). Click on the wallet you used to stake ICP and the NNS app will show you something like this: The transaction name should be “Stake Neuron” and under the “To:” field, you will see the wallet address for your staked neuron. 2. Send ICP to the wallet address we just found Click “New Transaction” and follow the prompts to transfer ICP from your NNS wallet to your staked neuron. Use the long string of characters we just found as the address to where you will send ICP. If you incorrectly type or copy this wallet address, you will send ICP somewhere other than your staked wallet and your token will be gone forever. So please be careful when you are pasting in wallet addresses. It is often a good idea to transfer a small amount first to make sure it works before you try to move serious amounts of ICP. There is a 0.0001 ICP fee to transfer ICP, but at the current price (~$50) that only amounts to half a cent in USD. 3. Refresh the app and make sure everything worked Now that we have transferred the ICP from our NNS wallet into our staked neuron we should be able to refresh the app to see our changes. It won’t refresh the amount of staked ICP in our neuron unless we refresh. Note that when you add ICP to an existing neuron you are setting it up with the same dissolve delay and locked/unlocked status of your existing neuron. And that’s it. You’ve staked more ICP in an existing neuron. Congrats!
Did you know, staking all of your ICP in the same neuron is advantageous because there is a 1 ICP minimum in order to stake ICP in a neuron and this limit applies to rewards as well. Which means you can’t spawn a new neuron until you have accumulated at least 1 ICP in rewards. So having all of your ICP in the same neuron means you will accumulate 1 ICP in rewards faster than if your ICP was spread out across multiple neurons. Getting rewards faster means you can disburse them and sell the ICP rewards for fiat, or like many bullish ICP investors, you can compound your returns by disbursing your rewards directly to your staked neuron to receive rewards more quickly.
Disclaimer, I own and stake ICP; this is not investment advice.