kalkül alternative
Backbone vs. kalkül: is paying worth it against a free tool?
kalkül is an Austrian invoicing tool from Linz whose core features are permanently free — a fair starting point for a one-person business that just needs BAO-compliant invoices. Worth knowing for context: kalkül advertises no AI features on its site, and reminders are sent manually.
Backbone (formerly Billy) starts exactly there: the AI assistant drafts invoices from one sentence and asks before sending, dunning adds statutory interest and the €40 flat fee where the law allows, and receipts, bank statements and a ZIP for your accountant come with it. Backbone also covers Austria AND Germany in one account — kalkül states an explicit focus on Austria alone.
Why freelancers move from kalkül to Backbone
A free tool gives you a form. Backbone gives you an assistant and a back office around it — dunning, receipts, time tracking — that keeps working after the invoice has gone out.
- An invoice drafted from one sentence instead of filling in a form — kalkül has no AI features
- Dunning with statutory interest and the €40 flat fee where the law allows it; stops when paid — in kalkül you click every reminder manually
- Recurring invoices — not advertised by kalkül
- Austria and Germany in the same account, mandatory-detail check under §11 UStG / §14 UStG while you write
- Receipt upload, bank statements and a ZIP for your accountant (with a free bookkeeper login) — not advertised by kalkül
Backbone vs. kalkül at a glance
| Backbone | kalkül | |
|---|---|---|
| AI & automation | ||
| Create an invoice from an AI prompt | YesBackbone AI, asks before sending | Nono AI features on the vendor site |
| Automatic dunning | Yesdunning with interest; own schedule from Studio | Noreminders are sent manually |
| Design & interface | ||
| Live preview while typing | Yes | Partiallylive preview in the design editor, not the invoice form |
| Custom branding | Partiallylogo, accent color, two templates | Partiallylogo free; colors & layout for paying supporters only |
| Invoicing workflow | ||
| E-invoicing (XRechnung/ZUGFeRD/ebInterface) | PartiallyZUGFeRD live; ebInterface & XRechnung coming soon | Nonot offered |
| Countries, bookkeeping & price | ||
| Austria | Yes§11 UStG check while you write | YesBAO-compliant, small business |
| Germany (§14 UStG) | Yessame account | Novendor states an explicit Austria focus |
| Price | from €19 / month incl. VAT, 7-day trial with card (€0 today) | core features permanently free; supporter subscription price not public |
kalkül pricing and feature claims per the vendor, verified on July 31, 2026, prices net. Backbone details per back-bone.io as of October 9, 2026; Backbone prices incl. VAT. Subject to change.
Backbone in detail
When kalkül is the better choice
To be fair: kalkül is a genuinely good free offer for a one-person business in Austria — invoices, the small-business rule, BAO compliance and even cash-basis accounting cost nothing, and the vendor commits to keeping existing accounts' free features free. If you write a handful of invoices a month, chase them yourself and work only in Austria, you do not need Backbone. And if you need an ebInterface file today, Backbone only has it coming soon.
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