Undertow

Undertow is a calculator for people paying off more than one debt. It answers a narrow question precisely: how much extra can I put toward debt this month without running my account dry before payday. THE PAYOFF PLANNER Add each debt with its balance, interest rate, minimum payment and due day. Switch between two orders with one tap: smallest balance first, or highest rate first. The payoff date, the months remaining and the total interest for each order appear side by side, so the choice is made on numbers rather than opinion. COMPARE THE TWO Both payoff curves are drawn on one chart. Drag the extra-payment slider and they redraw live, with a faint line showing where the previous amount would have taken you, and a plain sentence underneath saying what changed. THE CASH-FLOW FORECAST A projection of your balance over the next 30, 60, 90 or 365 days, built from your recurring income and expenses, one-off events, and every scheduled debt payment. A shaded band marks the cushion you set, so a dip below it is visible before it happens. SAFE MAXIMUM PAYMENT The app searches for the largest extra payment that never takes your projected balance below your cushion, and names the exact date things would go wrong if you paid more than that. WHAT-IF SANDBOX Press and drag on the forecast to try a hypothetical expense or a windfall and watch the curve react. Keep it as a real event or discard it. COLLISION WARNINGS You are flagged when a one-off expense lands in the same week as rent and a debt payment. THE DETAIL Recurring items can be paused instead of deleted. Payments are logged with their principal and interest split, each debt keeps its full history and the next three scheduled payments, and actual transactions re-anchor the forecast to reality. Fully offline. No account, no bank connection, nothing leaves the device. It is a calculator on numbers you type in, not a financial adviser: it makes no lending offers, credit recommendations or investment suggestions.