Rent versus own: the method behind the sums
Rent versus own arithmetic: the four things a calculator has to show, and the assumptions that quietly favour the subscription.
A rent-versus-own calculator is the easiest page on a software site to fake. Pick a flattering subscription price, multiply by a long horizon, put your own one-time price beside it, and the arithmetic does the selling. Every vendor in this position is tempted, and the temptation is why the method matters more than the output.
This page describes the method behind the calculator on this store: what it uses, what it refuses to do, and the assumptions it makes that quietly favour the subscription.
The four things a calculator has to show
The rented figure, with its source and its date. Not an average, not a typical, not a figure from a review site. The calculator here only includes a row where the competitor's monthly price exists as a cited figure with a live source link and a verification date -- if a vendor publishes no price, the row does not appear at all rather than appearing with a guess.
The owned figure, as actually charged. The one-time price for the same job, taken from the product's live single-licence price rather than from a marketing page.
The horizon, stated out loud. A subscription cost is meaningless without a number of months attached, and the number of months is a choice the reader deserves to see and change.
The assumptions, listed rather than buried. Every one of them is a place the answer could move.
What the calculator refuses to do
Two refusals are worth more than any feature.
It does not convert currencies. A row whose published price is in euros is dropped rather than shown as dollars. The reasoning is stated in the code that does it: a euro shown as a dollar is a fabricated figure even when the number itself is right, because the reader will compare it against dollars. Dropping the row loses information; converting it invents some.
It does not fill gaps. No estimate stands in for a missing price. A vendor who gates pricing behind a sales call is recorded as gated, and is not silently assigned a plausible number.
Both refusals make the table shorter and neither makes it weaker. The same arithmetic drives the page and the email version of it, so there is one calculation rather than two that can drift apart.
The assumptions that favour the subscription
An honest calculator names the ways its own comparison is generous to the other side.
The subscription price never rises. Multiplying today's monthly figure by the horizon assumes no increase across the whole period, which is not how software pricing has behaved.
The seat count never grows. A per-seat tool costs more the moment a fourth person needs access, and the multiplication assumes the team is frozen.
No add-ons. Second meters -- per resolution, per extra inbox, per transaction -- are common and are not in the monthly headline.
The owned side is not free either. Hosting costs something, your time costs something, and a one-time price is not a zero-cost column. The store has a whole page on that half: what self-hosting actually costs.
Read those four together and the direction is clear: the arithmetic understates the rented column and does not pretend the owned column is nothing. That is the right way round for a page published by somebody who sells the owned column.
How to run it on your own numbers
Take the horizon you actually plan for rather than the longest one available. Use your real seat count, including the people who need read-only access. Add your hosting figure to the owned side. Then look at the difference per month rather than the total, because that is the number your budget conversation is about.
If the answer is close, the subscription is usually the better choice, because a close call plus flexibility beats a close call plus a migration.
Questions people ask
Why are some vendors missing from the table? Because they publish no price, or publish it in a currency the page will not convert. Both are recorded rather than estimated, and an estimate would be a fabricated figure.
What horizon does it use? The horizon is visible and yours to set. A multiplication with a hidden period is the oldest trick on a page like this.
Does it pretend self-hosting is free? No. Hosting and your own time are real costs, and there is a separate page on precisely that so the comparison stays honest.
Where to look next
The calculator is at the calculator, the figures behind it live in the observatory with their read dates, and the owned side of any row is a product page -- Slotly and Rostera among them. For the honest account of what running your own copy costs, read what self-hosting actually costs. Prices are on the observatory; read them on the date shown there.
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