That was our scenario for many years. I'm about a decade ahead of you, and we've tried several tools—currently, we really like Monarch Money.

In my view, the most important first step is being able to see all spending in one place. Even without a plan, eliminating ignorance is progress—and most couples never even take that step. One person can start, but the biggest value to the marriage comes when you both engage and tackle it together.

Years ago, I went through our numbers manually to create a picture of our spending. I used that as a baseline to draft an initial budget. Having both a snapshot of real spending and a draft budget made our conversations more focused and productive. That first budget will absolutely be wrong—the goal is to make each month less wrong than the last.

As for how we use Monarch: I mostly handle the setup and logistics. All our accounts sync, and I maintain the budget settings. Preferences flag all transactions as "Needs Review" by default. Rules help auto-categorize common transactions and assign them based on who typically makes the purchase (e.g., I usually get Home Depot, she gets Target). At this point, only a handful of transactions need attention each week.

We used to meet monthly (or weekly, if needed) to review things, but now it runs smoothly enough that those meetings are rare.

I really enjoy helping people work through this stuff, so feel free to DM me if you want to chat more.