Behavior Shifts Unlock Bigger Markets Than Technology Shifts

01 /The Concept

The traditional playbook when couples get married: open a joint account, route income or a portion of it there, attach a shared card, and use it for household spending. Straightforward, if a bit formal.

But more people now want financial independence even within committed relationships. Joint accounts carry a weight – legal entanglements, shared liability, a level of financial merger that couples increasingly prefer to defer or avoid entirely. The trend is especially visible among couples who move in together without getting married, a demographic that has grown substantially and shows no signs of reversing.

For now, these couples manage shared expenses through a patchwork of workarounds: splitting bills via Venmo, tracking balances in Google Sheets, negotiating informally. It works, but it's friction.

Tandem is an app for "modern couples" that makes shared saving and spending feel as seamless as a joint account – without actually requiring one.

Each partner continues using their own card for everything. But they can tag certain recurring expenses (rent, Netflix) or individual purchases (dinner out, movie tickets) as shared. Those transactions immediately appear in the Tandem app for both partners, along with each person's share of the cost. Splitting rules can be set as defaults across all expenses, applied to specific categories, or adjusted manually for any single payment.

When it's time to settle up, one button in the app closes out all outstanding balances. Tandem calculates the net position – offsetting each person's debts against the other's – and transfers the difference to whichever partner paid more overall.

The app also includes a wishlist feature for things the couple wants but can't afford yet: a couch, a TV, a vacation. Items can be chosen from a partner marketplace built into the app. Once selected, both partners can set up automatic contributions from their individual accounts – in whatever proportion they've agreed on – going into a dedicated savings account that earns interest. When the balance hits the target, the purchase can be made in one tap through the in-app marketplace.

Tandem presumably earns a referral fee from those marketplace transactions – a revenue stream alongside its subscription fee of $12/month per couple (or $120/year).

The platform currently serves 25,000 couples who have collectively processed $60 million in shared payments and purchases.

The company just raised $3.7M, bringing total funding to $7.2M.

02 /Why It Matters

A [related review](/review/nekotorye-zhenjatsja-a-nekotorye-tak) from summer 2022 covered Ivella, a similar app for couples "at any stage of the relationship." Since then Ivella has added shared savings accounts for joint purchases – the same feature Tandem now offers – and has raised $4.5M.

Other apps with overlapping functionality have emerged too. What's driving this cluster of startups?

The answer lies in a behavioral shift that was already underway in 2019 and has only accelerated since.

Americans are choosing to live together rather than marry at increasing rates. In 2022, roughly 60% of Americans had been married at some point, compared to 54% who had cohabited without marrying. The prior decade saw those numbers flip: 59% had cohabited versus 50% who had married.

By 2022, more than 20 million Americans were in unmarried-couple households – triple the number a decade earlier.

69% of Americans now view cohabitation without marriage as completely normal. That means a large and growing share of households will face the practical challenge of managing shared finances without shared accounts – and without the legal structure that traditionally came with a joint account.

Interestingly, the primary reason couples who live together delay marriage isn't relationship uncertainty – it's financial unreadiness. People appear to be treating cohabitation partly as a financial compatibility test before committing to something more binding.

Even the core rationale for moving in together is often financial: splitting rent, sharing household costs, eliminating duplicate grocery runs. Which means there's real demand for financial tools that make that collaboration easy, transparent, and low-stakes.

The same problem shows up in a different form for separated couples with children. Shared expenses for kids require ongoing financial coordination between two people who no longer share a household or finances – and the solution is structurally similar. Startups like Onward have built purpose-built products for this use case – [covered in fall 2022](/review/100-milliardov-na-obshhih-detej) and [earlier under the name Ensemble](/review/my-vse-razvedjomsja) – raising $12.7M total.

03 /Opportunities

Startups tend to take off when they ride a shift that's already happening – in technology, in markets, or in how people behave. Founders have a well-documented bias toward technology shifts. Behavioral shifts get less attention, but they're equally valid launch vectors.

The rise of unmarried cohabitation is one such shift. Tandem and Ivella are riding it. But it's almost certainly not the only behavioral change worth paying attention to right now.

The most transferable insight here is a timing heuristic: find a behavioral shift that's already underway and build the adaptation layer. The shift itself is the tailwind – the product's job is to reduce the friction of adjusting to it. What shifts around you have already passed the tipping point but haven't yet been well-served by software?

If nothing immediately comes to mind, the space Tandem and Ivella are building in is genuinely underserved and growing – whether it's shared finances for cohabiting couples or co-parenting expense management. Both are real pain points that current tools handle poorly, and both represent meaningful product opportunities.