Rental Property Deal Analyzer

Most rental calculators exist to tell you a property is a good idea. They assume three per cent appreciation, grow the rent and hold every cost flat, and produce a number that goes up the further out you look.

This one starts every growth assumption at zero. The projection is flat unless you turn growth on yourself, and when you do, the insurance and the tax and the maintenance grow with the rent rather than staying politely still. A deal that only works with appreciation is a bet, and the tool will not disguise one as the other.

You get the four figures that actually decide it, updating as you type: cash flow after the loan and every running cost, cash-on-cash against the money you genuinely put in rather than the purchase price, cap rate unlevered so it compares against anything, and debt service cover, which is the one lenders look at and most buyers have never calculated. Move the interest rate and watch the cover fall — that is usually the moment somebody discovers the deal only works at a rate they are not going to get.

Underneath is ten years of it: cash flow, cumulative cash, the loan balance coming down, and the equity that builds from paying it off rather than from hoping.

Save as many as you like and put any two side by side, figure against figure, with the better one on each line marked and the difference in its own column. That screen is the one that decides things, and it is the part a free calculator cannot do at all.

It will not tell you what a property is worth or what rent you can get. It has no data on your area and does not pretend to. It takes your figures and does the arithmetic honestly, including the arithmetic that says no.

One HTML file. No account, no subscription, no internet needed. Opens on Windows, Mac and Android; the readme explains the extra step on iPhone and iPad, where Apple blocks JavaScript in downloaded files and every tool of this kind is affected.

Everything lives in your browser on your device. Nothing is uploaded, which is why it works offline and why nobody else can see your figures — and it also means clearing your browsing data deletes it. The tool does not pretend otherwise: the header shows how long since your last export at all times, turns amber after three days and red after seven, and export is one click that produces a plain file you keep.