Choosing a cash book app comes down to one question you answer before comparing a single feature: are you only keeping a cash book, or are you running an electronic till? A cash book records your cash movements, and a bookkeeping program is enough for that. An electronic till is a recording system under section 146a of the German Fiscal Code (Abgabenordnung, AO), and that requires a certified technical security module, a receipt for every transaction, and since 2025 a notification to the tax office. The German cash register regulation (Kassensicherungsverordnung, KassenSichV) explicitly excludes electronic bookkeeping programs, which is why DATEV Kassenbuch online, Lexware Office, sevDesk, WISO MeinBüro and Papierkram get by without a security module, as long as you use them to record the cash movement afterwards and do not take payment on them; a tablet till such as ready2order does need one. Once that is settled, four things decide: whether the app stores records unalterably, whether it exports into your bookkeeping, whether it works offline, and what it costs (as of September 2026). One sentence up front, because it matters more than once below: this is the law as written in the provisions named here, not tax advice for your situation.
Almost no cash moves through my own business; my case is card reconciliation. So this article stops at the point where the movement has been recorded. What happens after that, the screening and the sorting, has been handled since 19 August 2026 by Peter, my AI employee for receipts and bookkeeping. Which software suits your business overall is covered in Accounting Software for Small Businesses, and the groundwork before that in Bookkeeping Basics for the Self-Employed.
Cash book or till: the fork in the road
For cash, section 146 (1) AO comes first: entries and records must be made individually, completely, correctly, in a timely manner and in an orderly fashion, and literally: "Cash receipts and cash payments are to be recorded daily." That applies to anyone with a cash drawer, whatever the technology. There is so far no obligation to use an electronic till at all; the open cash drawer remains permissible, unlike in Austria, where a cash register obligation applies above certain thresholds.
If you do use an electronic recording system, section 146a AO adds three duties. Who counts is defined in section 1 KassenSichV: "electronic or computer-assisted till systems or cash registers". Explicitly excluded are ticket machines and ticket printers, parking and parking permit machines as well as charging points for electric and hybrid vehicles, electronic bookkeeping programs, goods and service vending machines, ATMs, and gaming and prize machines. Subsection 2 adds EU taximeters under Annex IX of Directive 2014/32/EU and odometers, including app-based systems where the app takes over exactly that function.
That exemption is why most cash book apps need no security module. What decides it is not what a product is called but what it does: section 146a (1) sentence 1 AO applies to whoever “records transactions subject to recording, or other processes, with the help of an electronic recording system”. If the app records the cash movement afterwards, in the accounts, the exemption applies; if it records the process itself, it does not. Taking orders and payments on a tablet or phone is the clearest sign of that, but it is a sign and not the criterion: the same app can sit on either side of the fork depending on how it is used.
A second difference follows from this. Under section 146 (1) sentence 3 AO, the duty to record each transaction individually falls away on grounds of reasonableness when goods are sold for cash to a large number of unknown persons. Sentence 4 withdraws that relief as soon as an electronic recording system is in use. Buying the till means giving up the simplification.
The three duties that come with a till
Certified technical security module. Section 146a (1) AO requires every transaction subject to recording to be recorded individually, completely, correctly, in a timely and orderly manner, and protected by a certified technical security module. It consists of a security module, a storage medium and a digital interface; certification is issued by the Federal Office for Information Security (BSI). Systems without that protection may not even be advertised or placed on the market.
Receipt obligation. Under section 146a (2) AO, a receipt must be made available to the other party in immediate temporal connection with the transaction. What it must show is set out in section 6 KassenSichV: the full name and address of the supplying business, the date of issue as well as the start and end time of the transaction, the quantity and type of goods supplied or the scope and nature of the service, a unique transaction number, the consideration and the tax amount plus the applicable rate or a note on tax exemption, the serial numbers of the recording system and of the security module, and a check value with a sequential signature counter. The receipt may be issued on paper, or electronically with the recipient's consent, for example as a QR code. Where goods are sold to a large number of unknown persons, the tax office can grant relief from the receipt obligation under section 148 AO on grounds of reasonableness.
Reporting duty. Section 146a (4) AO requires you to inform the competent tax office within one month of acquiring or decommissioning a system, by electronic transmission, naming the taxpayer, the type of systems and their serial numbers. That duty was suspended for years. Since 1 January 2025 the procedure has been available through "Mein ELSTER" or third-party software via the ERiC interface, using the form "Mitteilungsverfahren nach § 146a Absatz 4 AO". Systems acquired before 1 July 2025 had to be reported by 31 July 2025; since then the one-month rule applies from acquisition, and deregistration works the same way. Reporting is done per business premises, in a single notification covering every system there. If your practice software handles it, that can cost extra: DATEV lists the cash register notification at 10.00 euros per notification and Kassenarchiv online at 90.00 euros per till and calendar year (as of 08/2026, net).
This third point is the one people underestimate, because the till itself has long been running correctly. The notification is still a separate act, and nobody does it by accident.
Five criteria for the choice
- Unalterability. The test is section 146 (4) AO: a record may not be altered in a way that leaves the original content undetectable, or leaves it unclear whether the change was made later. A spreadsheet where you can overwrite rows does not meet that.
- Security module included or required? For a bookkeeping program: not required. For a till: mandatory, and then the question is whether it is in the price.
- Export and integration. Do the cash entries arrive as booking proposals in your accounts or as a DATEV export to your tax adviser, or does everything end up as a PDF?
- Offline use. Market stall, clubhouse, cellar. Cloud tools need a connection, device-bound apps do not.
- Price. Almost always the least important point, because the cash book sits inside a subscription you need anyway. It matters where a feature only unlocks at a higher tier.
The cash book apps compared
The second column reports what the vendors themselves say; used as a bookkeeping program, none of these apps needs a security module. No official approval stands behind any of these statements, and your cash book does not become proper through the product alone but through the whole path: setup, daily use, process documentation, export and retention.
Three cases follow. If your tax adviser works with DATEV, take Kassenbuch online, because it is included in DATEV Unternehmen online and the cash entries carry on as booking proposals. If you keep your own books, the cash book of the software you already pay for is the shortlist, not the decision; you still check the tier (Lexware Office from version L, WISO MeinBüro from the Buchhaltung plan, Papierkram already in the free plan), unalterability, export, access rights, backup, and whether your tax practice can work with it. If it is only about having an overview, a private household cash box or the non-commercial side of a club, a device-bound app such as Kassenwart or Das Kassenbuch is enough, and the fact that neither vendor claims GoBD compliance and the export ends as a CSV or PDF file does not matter there. That third case, though, is not decided by legal form or by how much time you spend on it, but by the activity: wherever a commercial operation within the meaning of section 14 AO sits behind it, in a club as much as in a sideline, the same recording duties apply as in any main business, and you choose by the five criteria above.
When it does have to be a till
If the app records the process itself, the three duties above apply and the comparison shifts. ready2order integrates the security module as a cloud TSE from its partner fiskaly, certified by the BSI on 28 May 2021, and needs no extra hardware for it. It is not part of the standard subscription, though, but a separate annual one: the vendor page lists 35.90 euros a month for the till subscription and 15.90 euros for the TSE package, plus a complete hardware bundle from 399 euros. The DSFinV-K export for an audit and a DATEV export are available, and when the internet fails an emergency mode keeps running, logging the outage in the TSE protocol and showing it on the receipts. SumUp sells its till as hardware from 249 euros with software plans from 0 euros and a Plus plan at 49 euros, with transaction fees of 1.39 percent or 0.79 percent on the Payments Plus plan, and advertises that it takes care of TSE compliance. In both cases the notification under section 146a (4) AO stays your job, not the manufacturer's.
What is about to change
On 7 August 2026 the German Federal Ministry of Finance published a draft bill that would require businesses with more than 100,000 euros in annual turnover to use an electronic recording system with a certified security module from 1 January 2028. The open cash drawer would no longer be permitted for them, while it would remain permitted below that threshold. At the same time the paper receipt obligation would be replaced by electronic provision, for instance via QR code or NFC, with the customer's civil law claim to a paper receipt left intact. This is a draft, not a law (status: 19 September 2026). For choosing an app today it means one thing only: if you are anywhere near that turnover threshold, pick something you can get your data back out of.
What comes after recording
The app gets the cash movement into the system. Then the work starts that no till function takes over: every receipt needs the right document type, every line on a statement needs its receipt, and every discrepancy needs a decision.
That is exactly where Peter starts in my business. He screens what is already recorded in the system, assigns the correct document type to each receipt, and matches the credit card statement against it line by line. He works in my real bookkeeping interface in the browser and follows a written process description; what is not in it, he does not do. I published the numbers from his first run myself: 116 receipts screened, 38 of 40 assigned correctly, a good hour. On his second run in September he had 68 receipts in the queue, checked 54 of them, and the control export afterwards showed zero discrepancies.
The two open ones matter more to me than the 38 he set. They stayed open because his process could not decide the case unambiguously, and he reported them as open instead of making them fit. With cash that matters even more than with cards: a till discrepancy is a finding you record, not a rounding error you smooth away. What AI actually delivers in bookkeeping today, and where its limit sits, is in AI Bookkeeping: What Actually Works Today, and the setup behind it in AI Agent for Bookkeeping and Inbox.
Frequently asked questions
Which cash book app is the best?
The one belonging to your bookkeeping. It stores records unalterably, produces the cash report and passes the data to your tax adviser without retyping. If your practice works with DATEV, Kassenbuch online is the obvious choice. Otherwise you start with the software you already pay for and check the five criteria against it.
Is there a free cash book app?
Yes, with limits. Papierkram includes the cash book in every plan, including the free one, though with a maximum of one till per account. Kassenwart is free and works fully offline, but claims no GoBD compliance. Das Kassenbuch for iOS costs 1.99 euros once. For a cash drawer in a real business, the export into your accounts matters more than the price (as of September 2026).
Do I need a TSE for a cash book?
No, not if you only keep a cash book. Section 1 KassenSichV explicitly excludes electronic bookkeeping programs from the definition of electronic recording systems. You need the certified technical security module under section 146a (1) AO only once the system records the process itself instead of booking the cash movement afterwards.
Do I have to report my till to the tax office?
Yes, if it is an electronic recording system. Under section 146a (4) AO you report acquisition and decommissioning within one month by electronic transmission, since 1 January 2025 through "Mein ELSTER" or the ERiC interface. Systems acquired before 1 July 2025 had to be reported by 31 July 2025. A plain cash book inside bookkeeping software is not subject to the reporting duty.
Is a cash book app approved by the tax office?
There is no official approval for individual programs. What counts is whether the records meet the requirements, above all unalterability under section 146 (4) AO and daily recording under section 146 (1) AO. “GoBD-compliant” on a product page is a vendor statement, not a certificate from the tax office. Whether your specific setup is sufficient is a question for your tax adviser.
Can I use a cash book app for a club or privately?
Privately you need no cash book in the tax sense; that is about having an overview, and a simple app on the device is enough. In a club it depends on the area: for the non-commercial side there are dedicated apps with member management and receipt numbering. Where a commercial operation within the meaning of section 14 AO sits behind it, in a club as much as in a sideline, the same recording duties apply as in any business: the activity decides, not its size.
How to take this further
Answer the fork from the first section first, in writing: does the system record the process itself, or do I record cash afterwards? Most wrong purchases start exactly here.
If you only keep a cash book, test it for a week in daily use rather than against a feature list: record the till every day, produce the cash report at the end of the week and count the cash against the balance in the cash book. If the number does not match, you will see immediately whether the app shows you the difference or papers over it. The test shows you usability and gaps in the process; whether your records meet the requirements is a question that stays with your tax practice. If you run a till, check three things on a quiet morning: is the security module active, can you produce the DSFinV-K export, and has the notification gone to the tax office.
Then there is the work that comes after: sorting, matching, reporting discrepancies instead of calculating them away. How I handed that part to an AI employee, with a written process description, a learning mode and a control count before and after, is what I show in my community Claude Practitioners. What an AI employee is in the first place is on the page on hiring an AI employee.
