InterestThing

TVM, IRR & Cash Flow Solver

Only for Mac

Free

Mac

Explore InterestThing free — full functionality for educational use. Use InterestThing to track live loans and leases — not just calculate them. By combining events and compute options, it handles everything from a simple interest calculation to complex cash flows, leases and valuations — with results most financial calculators simply can't match. HOW IT WORKS Unlike template-based calculators, InterestThing lets you define the problem yourself as a timeline of events. Each event is a cash flow — an inflow, outflow, unknown, fixed principal, or interest-only payment — or a modifier such as a rate change or balance date. Events can occur once or repeat periodically, with amounts that remain fixed or evolve using arithmetic or geometric gradients. Each event creates one or more rows in the schedule — combine them to model any financial problem. Each cash flow is further defined by its compute options: choose any of four interest types — simple, capitalised simple, capitalised simple with US Rule, or compound — and combine it with any of three time interval methods: year fraction, periods and days, or periods and days with reference date capitalisation. Each method supports its own set of day count conventions. Any combination is valid. REAL-WORLD EXAMPLES Loan or mortgage: add an outflow for the loan amount, followed by a series of unknown payment events. InterestThing solves the payment. Lease: add events for advance, step-up, regular, step-down and residual payments with weighted unknown factors — InterestThing solves the single multiplier that satisfies the entire cash flow. Construction loan: first solve using regular payment dates to plan the loan, then replace events with actual amounts and dates to track it against reality — with interest capitalised on reference dates throughout. Financial planning and valuation: model any combination of future cash flows — solve for required savings, regular withdrawals, or the present value of any investment. WHY INTERESTTHING GETS THE MATH RIGHT Most financial calculators capitalise or compound interest on payment dates, silently introducing implicit compounding errors. InterestThing solves this with reference date compounding and capitalisation — interest is either capitalised on the reference date or kept pending until the next one, giving you mathematically correct results regardless of cash flow structure. Balance dates: insert as many as you need anywhere in your cash flow to see the outstanding balance at any point — without affecting the calculation. NO BLACK BOX CALCULATIONS Every schedule row shows the full breakdown — accrued, capitalised and pending interest, outstanding principal, interest due and total due. The Details tab breaks down every event into its reference dates, period and day fractions. The Summary tab gives a complete audit trail: all compute options, applicable rates, event statistics, cash flow duration and dominant interval, and the exact denominators occurring across the entire cash flow — with their respective counts and percentages. Nothing is hidden. FEATURES Cash flow events: inflows, outflows, unknowns, interest-only, fixed principal, rate changes and balance dates. Single or periodic, with arithmetic and geometric gradients. Interest types: simple, capitalised simple (with and without US Rule), and compound. Time between dates: calculate as a year fraction using any of 18 day count conventions — including Act/Act, 30/360, ISDA, AFB and Eurobond — or as a periods fraction and a days fraction using any of 20 conventions, including 2 additional ICMA period-based methods. Tools: rate conversion, day count comparison, and period/day analysis. If you can define the problem, InterestThing can solve it.

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Version 1.0

Version 1.0

The developer, Patrick Jan Van der Perre, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .

  • Data Not Collected

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    Information

    Seller
    • Patrick Jan Van der Perre
    Size
    • 3.8 MB
    Category
    • Finance
    Compatibility
    Requires macOS 13.0 or later.
    • Mac
      Requires macOS 13.0 or later.
    Languages
    • English
    Age Rating
    4+
    Copyright
    • © 2026 ParanzaSoft - Patrick Jan Van der Perre
  • Privacy Policy

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