Most budgeting apps that let you “test a scenario” first ask for your bank login. The pitch is that connecting an account gives the simulator real numbers to work with. What it actually gives a third party is a live pipeline into your bank — just to answer a question you could answer with five numbers you already know.
Recurna Flow’s what-if sandbox works the other way. You never connect a bank account to use it, and testing a decision does not touch your real forecast until you decide it should. This guide covers why that combination — no bank connection, no permanent change — makes the sandbox something you can actually trust, not just something that happens to be private.
Why the two are the same problem
A what-if only tells you something useful if you believe the number it produces. That belief breaks down for two different reasons, and a private budget app has to solve both:
- Trusting the input. If testing a decision required linking your bank, you’d be handing a login to a tool just to ask “what if I take this raise?” The sandbox does not need your transaction history to answer that — it needs the raise amount, your existing recurring bills, and your current balance. You already have those numbers.
- Trusting the sandbox stays a sandbox. A what-if is only safe to explore if changing it can’t quietly become real. If a decision tool writes to your actual data as you experiment, you stop experimenting freely and start being careful — which defeats the point of a sandbox.
Recurna Flow’s simulation mode is built around both: it runs entirely on the forecast you already have — built from what you told the app, not from a bank feed — and every adjustment you make inside it is layered on top, never written back until you say so.
Model it in Flow
Any what-if — a raise, a new subscription, a rate change on an existing loan — follows the same path, and none of it requires linking an account.
- Open the Forecast page and set the account scope to the account the change affects. Set the date range to Next 1Y to see the full effect.
- Open the simulation panel from the Forecast page. The sidebar slides in
and the URL gains
?sim=1— this is your sandbox, separate from your real data. - Tap + to open the Add adjustment sheet. Choose Start from scratch.
- Pick the adjustment type that matches your what-if — New Recurring for an ongoing change like a raise or a new bill, One-time for a single event like a bonus or a big purchase.
- Fill in the amount, the account it affects, a short description, and — for a recurring change — the frequency and start date.
- Tap Add. The forecast redraws with the adjustment included, and the chart shows the week-by-week effect immediately.
Nothing in these six steps asks for a bank login, and nothing you build here changes your real forecast. You can add three different raises, delete all of them, and try a fourth — the sandbox does not care, because none of it is written back until you leave it that way on purpose.
Read the forecast, then decide
Look at the week-by-week breakdown, not the average. Find the lowest projected balance across the year — that trough is the real answer to “can I afford this,” whether the change is a raise, a new recurring bill, or a loan you’re considering. If the trough stays comfortably above your floor, the change fits. If it dips close to zero in a specific week, you now know which week to watch for before you commit to anything.
Saving a simulation and comparing two side by side are Pro features. On the free tier you can still build any what-if and read its effect on your 12-week forecast — the sandbox itself has no bank-connection requirement at any tier.
When you exit simulation mode, your real forecast is exactly as you left it. The what-if only becomes real when you rebuild it as an actual recurring transaction or bill — a separate, deliberate step.
Why manual-first makes the sandbox honest
The same design choice that keeps your login private also keeps the sandbox trustworthy: your bank credentials never leave you, and your transaction data never reaches a third-party aggregator, because there is no sync step to begin with. Everything the simulator uses — your recurring income, your bills, your current balance — is what you entered, which means you can see exactly what went into any number it shows you. There’s no imported data you didn’t put there yourself, and no external service quietly watching the account while you experiment with it.
That’s the whole point of a private budget app: not just that your data stays under your control, but that a tool built that way has no reason to make “testing a what-if” cost you your bank login.
Want the full year of runway, not just 12 weeks, and the ability to compare two what-ifs side by side? That comes with Recurna Flow Pro.