If you had $18000 dollars and had the option of investing it all and paying tax later or paying tax now and investing the rest, you'll end up with the same amount.
If you have $24000 to invest, your two options are:
1. Invest $18000 in a 401k, pay tax on it later. Pay tax on $6000 now, invest the rest and pay tax on the gains later too.
2. Pay $6000 in tax now, invest $18000 in a Roth account, pay no tax on it later.
The second one is better because it's essentially letting you put more of your earnings into the tax-advantaged account.
If you have $24000 to invest, your two options are:
1. Invest $18000 in a 401k, pay tax on it later. Pay tax on $6000 now, invest the rest and pay tax on the gains later too.
2. Pay $6000 in tax now, invest $18000 in a Roth account, pay no tax on it later.
The second one is better because it's essentially letting you put more of your earnings into the tax-advantaged account.