Having too much cash in your portfolio can dilute your gains, while not having enough cash in your portfolio can impede you from making investments. How much cash do you need in your portfolio?
There are several factors you need to consider and most of these are regarding your personal finances and risk tolerance. If you can constantly add cash to your portfolio, you may not need to keep much in cash.
The most important factor to consider, in my opinion, are valuations of the S&P 500 $SPX500 . If the market is overvalued, you may want to have more cash ready for a crash. But if the market is undervalued, you should be investing.