You are each entitled to one-half of the other’s retirement assets that was accumulated during the marriage (date of marriage to date of separation). In practice, you would combine these so you’re not having to divide two accounts and retirement assets going from Husband to Wife and Wife to Husband (see example below).
You are not legally bound to equally divide retirement assets. You can waive the ability to obtain one-half of the retirement assets, especially if you each have relatively equal retirement account balances or there isn’t much to divide.
You are not entitled to any retirement assets of your husband’s that he acquires after the date of separation. Anything acquired after the date of separation in his account is his separate property.
To equalize retirement assets instead of dividing multiple accounts, take for example that you have $50,000 in your 401(k) and your husband has $100,000 in his 401(k) at date of separation and all of the assets were acquired during the marriage. Your husband would owe you $25,000 in retirement assets in order to equalize the retirement distribution so that you each end up with $75,000 in retirement ($100,000 - $50,000 = $50,000 / 2 = $25,000 (one-half the difference)).