Just thinking about my tax return and was just wondering about the sending of all the end of year certificates for each bank account.
I always wonder, if you don’t include an account, would they know? Do Swiss banks tell them about all your accounts? Or do they rely on honesty?
I have no intention of hiding any, I don’t have enough money to make it worthwhile anyway 
I’m just curious as to how it works.
Perplexity says
Banks now share account information with tax authorities through the Automatic Exchange of Information (AEOI), a global standard set by the OECD. This system requires financial institutions to report account details annually to their local tax authorities, which then share the information with the tax authorities in the account holder’s country of residence. Key information shared includes:
Identification details: Name, address, date of birth, and tax identification number.
Account details: Account number and financial institution’s name.
Financial data: Account balance, interest, dividends, and other income.
This process aims to prevent tax evasion by ensuring transparency across borders. Additionally, countries like the U.S. use the Foreign Account Tax Compliance Act (FATCA) to gather information on U.S. taxpayers’ foreign accounts.
That’s an awful lot of info to send every year - and also have the tax payer send a copy too. If the banks send it all already, why do we duplicate that info? 
There is still “Inland” banking secrecy in Switzerland, the Swiss banks won’t share your info with the Swiss tax authorities, at least proactively, not sure if that still holds if there’s a criminal investigation against you.
That is for Swiss residents, not all account holders. And Swiss banks will report account information to the US IRS for US citizens and residents.
I assumed the OP was a Swiss resident, yes. If a Swiss bank knows that you’re a tax resident of another country participating in AEOI they will send a report to the tax authorities of that country every year. Just not to Switzerland.
Yeah, sorry, to clarify, I’m talking about Swiss banks/accounts of Swiss citizens living in Switzerland.
Not only must one report each account, but also any cash that may lay under the mattress or the carpet.
Ok, I found this;
Swiss Bank Secrecy Explained - moneyland.ch.
" For bank customers who are fully tax resident in Switzerland, the rules below apply.
When a resident does not declare bank accounts and custody accounts at Swiss banks in their tax returns: The tax office does not receive any information from banks. Banks may not respond to any form of inquiries about whether the taxable person holds accounts with them."
So they are relying on your honesty.
The Swiss banks also charge a Verrechnungssteuer of 30% if your deposit yields more than 200 CHF of interest in a year, which you can only claim back (=deduct from taxes to pay) if you declare the account in your tax return.
Although there is no automatic exchange of information, they have made it attractive for you to want to report it :
Note that the cantons don’t ask for the bank certificates each year.
Nonetheless, in my experience they don’t allow quiet disclosure : if one year you specify that you closed the account, or that you have opened the account, they will require proof of that. Otherwise, it seems they just just check (ask for end of year statements) some people at random.
So if it is not attractive there is no need to report?
35%
basically, yes. And the past years it never was attractive, was it. And still ain’t. But you’re also avoiding paying wealth-tax on it, which also is peanuts. So imo cheating is not really worth it as the punishment if found out might be harsh, they may not care about the amount but the offense.
In 2003 we inherited from an uncle who had a few “black” accounts and even shares. To be honest I think it was just a little naughty sport of his. However, we as heirs decided to declare it all, no punishment for us, we only had to pay the tax on it in retrospect.
Everybody has that option, it’s called Straflose Selbstanzeige, and it’s far from rare to be used in inheritance cases. You (or the heirs) get billed for the ordinary tax amount ten years back plus interest.
Your first selfreport is free, any additional selfreports come with a fine of 20% of the tax evaded.
I agree that banks don’t send info about swiss tax residents accounts to the government, so if it is not worth even declaring (f.e. below 125k threshold in SZ), then i never bothered, situation changed only last few years when there was some interest > 200chf earned, so yes to return deducted 35% on that i did declare, but now interest dropped again, so this year won’t worth the hassle again
Swiss Banks won’t share your info with Swiss Tax authorities (That’s illegal), however they will share to foreign tax authorities if they believe you are resident abroad.
I had the impression that the Swiss law specifically changed in that matter in last few years. In previous canton I didn’t even have to include the bank statements anymore, so I guess they already had it (or maybe indeed it’s enough for them that they have the right to ask the bank at any time).
Moneyland thinks not Swiss Bank Secrecy Explained - moneyland.ch.
Historically it was illegal for a Bank in VD or GE to give evidence wvwn with a court order, some cantons require a court order others not, however only if a ‘;criminal offence is involved’ & tax evasion below CHF 300k a year is not a crime, just an administrative procedure.
I don’t believe anything has changed for Swiss residents.
Or if they know you’re American, they will share with Uncle Sam as required under FATCA. 