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Swell

Household money, without the spreadsheet.

Swell is a finance manager for households that share money. It pulls in bank and card transactions, sorts them, splits shared costs fairly, and tells you once a month who owes whom.

Get early access

Coming soon as a paid service. In private testing now.

One month in Swell, from the bank to closed books

  1. Bring it in

    • Banks over FinTS
    • Credit cards
    • Payments and brokerage
    • CSV uploads
    • Cash, from the phone

  2. Import

    Duplicates caught, foreign currency turned into euros.

  3. Sort

    Transfers set aside, then learned rules, then Claude.

  4. Split

    Shares per category, versioned by date.

  5. Settle

    One line: who pays whom, and how much.

  6. Audit

    Swell checks its own books.

  7. Close

    The month is frozen.

When it’s unsure, it asks. Possible duplicates, unmatched transfers, missing exchange rates and low-confidence categories wait in one review inbox for a person to decide.

If you share costs, there’s probably a spreadsheet.

Every month you type in the expenses, work out who paid for what, split the costs by the rules you agreed on, and settle the difference. It works. It’s also manual, easy to get wrong, and it never shows the bigger picture: net worth, paying off debt, retirement.

Swell does the same job without the typing. Transactions come in from the bank, your rules are applied for you, and the month ends with one line you can both trust.

It imports, sorts, splits and settles. Then it shows you the bigger picture.

Bring the money in

Only the banks’ own channels. No third-party aggregator.

  • German banks and credit cards over FinTS, the banks’ own standard. You approve each sync in your banking app.
  • Payment and brokerage accounts sync by themselves every day, including family accounts with sub-accounts.
  • CSV for everything else, with a saved column mapping for each account. German formats like 1.234,56 and 31.12.2025 just work.
  • Cash goes in through a quick-add form made for the phone, because that’s where cash gets logged.
  • Importing the same statement twice never creates duplicates. Near-duplicates, like a pending card charge that later posts, go to the inbox instead of being merged quietly.
  • Foreign currency becomes euros at import, at the source’s own rate where it has one and the ECB rate otherwise. The original amount is kept.

Sort it

Rules first, the model second, and a person when it’s unsure.

  • Transfers between the household’s own accounts, like paying off the card from the current account, are spotted and kept out of spending.
  • Learned rules go first. Claude, Anthropic’s AI model, categorizes what’s left.
  • Any correction can become a rule in one click, so the model gets asked less and less.
  • Setup groups the first import by merchant. Accept the proposals, or type something like “groceries are 60/40, but that shop on Saturdays is for my parents”, and Swell turns it into rules.
  • One review inbox holds everything that needs a human.

Split and settle

The rules you agreed on, applied the same way every month.

  • A split rule for each category: shares that add up to 100%, or personal.
  • Rules are versioned by date, so changing a ratio never rewrites history.
  • Refunds reverse the original split automatically.
  • Money put into a child’s savings account is split like any other shared cost.
  • Once a month, one line: who pays whom, and how much.

See the bigger picture

What the spreadsheet never showed.

  • Recurring payments, with an alert when one is missed or changes.
  • Budgets per category, without envelopes or rollover.
  • A debt payoff plan with a date for each debt, comparing avalanche and snowball.
  • Cash flow, savings rate, and net worth over time.
  • Brokerage holdings and returns, both time-weighted and money-weighted. Salary history and equity grants, including private-company options in a foreign currency.
  • A retirement calculator with a safe-withdrawal view, a die-with-zero view and Monte Carlo success bands. It never invents historical market data.

Let agents help

Ask, log and fix, with every change on the record.

  • AI agents such as Claude can connect to Swell to answer questions like “how much did we spend on eating out this quarter?”, log a cash purchase, or fix a category.
  • Each agent gets its own access, read-only or read-write, and you can revoke it at any time.
  • Every change an agent makes is logged under its name.

Before a month closes, Swell audits its own books.

The sheet trusted whoever typed last. Swell checks the month first and closes it only when the numbers hold up. Closed months are frozen, and anything that arrives late rolls into the next open month.

SettlementSeptember, an example

Partner A pays Partner B €132.40

Partner A
−€132.40
Partner B
+€132.40
Sum
€0.00

Month-end audit

  • Balances reconciled with every account
  • Card statements tied to the payments that cleared them
  • No one-sided transfers
  • No missing imports
  • Settlement sums to zero
  • One unusual charge, flagged for a look

Made-up numbers. The checks are real.

Coming soon.

Swell will be a paid service. It’s in private testing now. If you’d like to try it early, or hear when it opens, email us.

Ask for early access

contact@lunarmachinery.com