InterestLab

InterestLab is a financial calculator toolkit for everyday money decisions — from mortgages and loan payoffs to savings, interest rates, and dates. Fully offline.

InterestLab is a complete financial calculator toolkit for everyday money decisions — from mortgages and loan payoffs to savings, interest rates, and dates. Clean, fast, and fully offline.

Whether you're comparing a home loan, planning to pay off a credit card faster, or projecting how your savings will grow, InterestLab gives you clear numbers, helpful charts, and a shareable PDF — all in seconds.

WHAT YOU CAN DO . Mortgage — Enter the home price, down payment, rate, and term to see your monthly principal & interest, total interest, payoff date, a balance-over-time chart, and a full amortization schedule you can export as a PDF. . Loan Payoff — See how long until a balance is paid off and how much interest you'll pay. Add an extra monthly amount to see the time and interest you'd save. . APR ↔ APY — Convert between the nominal (APR) and effective (APY) annual rate for any compounding frequency — the fast way to compare loan and savings offers. . Savings with Deposits — Project growth with recurring monthly deposits, an optional yearly deposit increase, and inflation. Watch it build with a growth curve and an invested-vs-earnings breakdown. . Fixed Income — Model a lump-sum investment over days, months, or years, with inflation-adjusted results. . Loan Rate Finder — Discover the true interest rate hidden in a set of fixed payments — perfect for comparing financing offers. . Variable Income — Track gains and losses on any asset from purchase to sale, with daily, monthly, and annual rates. . Gains (Run-up) & Losses (Drawdown) — Understand the percentage needed to recover a loss, or given back after a gain. . Equivalent Rates & Stated Rate — Convert rates between periods and work with stated/effective rates (SAR / ER). . Dates — Days between two dates (calendar and business days), add or subtract time, and track ages, events, and anniversaries. . History — Save any calculation, search your records, and export or share results as a clean PDF.

BUILT FOR PRIVACY InterestLab works fully offline. There are no accounts, no sign-in, no ads, and no tracking. Everything you calculate and save stays on your device — we never see your data.

SIMPLE, POLISHED, FAST A tidy home screen, native charts, haptic feedback, Dark Mode, and Dynamic Type support make InterestLab a pleasure to use on any iPhone.

PREMIUM (OPTIONAL) The free version covers everyday calculations. A single one-time purchase unlocks unlimited terms for long-range projections — no subscription, ever.

Disclaimer: InterestLab provides estimates for informational purposes only and is not financial, tax, or legal advice. Always verify results and consult a professional before making financial decisions.