DINK is a popular acronym in the financial and FIRE community that stands for dual income, no kids. There's also DEWK which stands for dually employed with kids. Sadly there hasn't been an acronym for the situation my wife and I find ourselves in. I'd like to introduce SICK which stands for single income, crapload kids. With the recent addition of twins to our family we've become SICK.
Getting married with both partners working can be a great financial move. Your income increases but not all of your expenses double (think housing). You're also able to save 2x the amount into your 401(k) plans since a non-working spouse doesn't have this employee sponsored benefit.
That's not to say that you can't build wealth for retirement as a single income family. Yes, even if you have crapload kids. It does, however, take planning and dicipline. You'll want to maximize your retirement contributions and follow a budget.
The benefits that your employer provides will determine a lot of your retirement investment options. If your employer does not provide many of these options then consider looking for an employer who does.
It's important to max out your 401(k) since you only have one. Ideally your employer matches some of your 401(k) contribution. Even if they don't match you should contribute the maximum of $19,500 per year.
Both you and your spouse should open a Roth IRA and contribute the maximum allowed each year ($6,000 each in 2021, $12,000 total). Do this every year.
There are income limits you have to fall under in order to contribute to a Roth IRA. If you earn too much you can still contribute to your Roth IRA but you'll have to do it using a backdoor Roth.
Some employer plans support what's called a mega backdoor Roth (what is a mega backdoor Roth?). This lets you add up to $58,000 to your 401(k). Read the article which explains the mega backdoor Roth and find out if your employer's plan supports this.
An HSA can be used as a retirement account for medical expenses. HSAs are paired with high deductible health plans so you'll need to decide if that's best for your family. If it is then you can contribute a max of $3,600 per person or $7,200 (and an additional $1,000 per person over the age of 55). HSAs can be opened even if your employer doesn't offer one but the health plan your on needs to qualify. Make sure that the money in your HSA is invested in good stocks (like, low cost ETFs).
Bonus if your employer contributes to your HSA.
Controlling your spending is critical because you'll have increased expenses to take care of a family but only one income. Budgets get a bad reputation for being restrictive and soul crushing. But, if done properly, it can make it more enjoyable to spend money. Our budgeting app, Spend, is an example of how budgeting increases your happiness and improves your marriage (no joke).
Every dollar you save by budgeting is an extra dollar you can invest. That dollar will multiply several times by the time you're ready to use it. So it's more like spend a dollar today or save $5 for retirement.
It's possible to build wealth on a single income even if you have a family. You'll just need to pay more attention and make use of all the tools available to you. There's no better time to start than today!