Compare paying once for an app versus a subscription.
A one-time licence is a fixed cost; a subscription is a recurring one that keeps climbing. Dividing the purchase price by the monthly fee gives the break-even month — the point after which owning is cheaper. Comparing both totals over the months you realistically expect to use the app (plus any paid upgrades for the owned copy) turns a vague preference into an arithmetic answer.
Break-even month
Break-even months = one-time price / monthly fee; subscription total = monthly fee x months used
Divide the one-time price by the monthly subscription fee to get the break-even month, then multiply the monthly fee by how long you will actually use the app. If that subscription total exceeds the purchase price plus any paid upgrades, buying once wins.
Perpetual licences often go stale: major versions are sold again. Adding an annual upgrade allowance keeps the comparison honest, because a subscription usually includes those updates.
Yes. Below the break-even month the subscription is always cheaper, which is why trial projects and one-off jobs favour renting software rather than buying it.