Comerica positive pay file: building the check issue file

Comerica's positive pay service catches fraudulent and altered checks by comparing every check that hits your account against a list of checks you actually wrote. That list is the check issue file. You upload it through Comerica's treasury platform, and when a presented check does not match what you sent, the item is flagged for you to pay or return.

The work that trips most people up is producing that file in the exact format Comerica expects. This page explains where the Comerica file spec comes from, how the general workflow runs, and how to convert your check register into a matching file without buying desktop software.

What Comerica offers

Comerica groups its check-fraud tools into a few related products, and which one you have changes how you handle the issue file:

• Positive Pay. The standard service. You send Comerica a check issue and void file. Incoming checks that do not match are presented to your team online, often with check images, for a pay or return decision.
• Reverse Positive Pay. Comerica describes this as a fit for lower-volume check writers. Instead of sending an issue file up front, you review the checks that posted and flag anything that does not belong. Less setup, but more daily review on your side.
• ACH Positive Pay. A separate tool for monitoring and accepting or rejecting incoming ACH debits. It does not use a check issue file, so the format details below do not apply to it.

Access runs through Comerica's commercial platforms. ACH Positive Pay is delivered through Comerica Treasury Management Connect Web, and check positive pay is reached through Comerica Business Connect, the single sign-on portal for treasury services. If you are not sure which entitlement you have, your Comerica treasury contact or relationship manager can confirm it.

Where the Comerica file spec actually comes from

Comerica does not publish its positive pay check issue file layout on its public website. The exact record format, the field order, whether the file is fixed-width or delimited, and how dates and amounts must be written are provided during treasury onboarding, through your implementation specialist or inside the Business Connect or Treasury Management Connect setup materials.

This matters because we will not guess at it. Inventing field positions for a bank that has not published them is how you end up with a rejected file and a frustrated implementation call. If you do not have the spec yet, request it from your Comerica treasury contact before you build anything. It is typically a one or two page document that lists each field, its width or delimiter, and the order the columns must appear in.

That said, almost every positive pay issue file, Comerica's included, is built from the same handful of fields:

• Account number
• Check (serial) number
• Check amount
• Issue date
• An item type or void flag, so issued checks and voids are distinguished
• Payee name, when the bank uses payee positive pay

If your spec includes a payee name field, that means Comerica is matching the payee line too, which catches altered payee names but also means a typo in your register can flag a legitimate check. Keep your check register clean.

The general workflow

Once your account is set up for positive pay, the routine is the same on most banks:

1. Print or record your checks for the period, just as you normally would.
2. Export a register of those checks with the issued and voided items.
3. Convert that register into Comerica's required layout.
4. Upload the file through Business Connect, or transmit it on the schedule Comerica set up for you.
5. Each day, review any checks that did not match and submit pay or return decisions before the cutoff.

The decision deadline is the part to watch. Items left undecided past the daily cutoff follow a default rule your account is configured with, either pay or return. Know what your default is.

Converting your register into a Comerica file

QuickBooks, Xero, and most accounting systems will not export a positive pay file on their own. QuickBooks can produce a check register or a transaction report, but turning that into a bank-specific issue file is a separate step. That gap is the entire reason positive pay file tools exist.

PositivePayMaker is a free, browser-based converter for exactly this step. You upload your check register as CSV or Excel, map your columns to the fields Comerica wants, and it writes the file. Because Comerica does not publish a fixed public layout, you use the custom format builder to match your onboarding spec: set the field order, choose fixed-width or delimited, set the date and amount formats, and save it so you do not rebuild it every month. A generic CSV or fixed-width preset is a good starting point if your spec is simple.

Everything runs inside your browser. Your check data, account numbers, amounts, and payee names never leave your computer or get uploaded to a server. For account-level data like this, that is worth caring about. You can read more about how positive pay file formats are structured if you want to understand the spec before you map it.

Paid alternatives, and when they make sense

If you process high check volume or want a vendor on call, a few paid desktop tools cover positive pay:

• Big Red Consulting Positive Pay File Creator. Around $119 the first year, then about $99 per year. Windows only, and the QuickBooks Online edition needs Excel installed.
• Treasury Software Bank Positive Pay. Installed Windows software with a large library of bank layouts, roughly $30 to $90 per month depending on the plan.
• MoneyThumb and ProperSoft sell paid desktop converters as well.

These can be worth it if you need a maintained library of layouts, run Windows, and would rather pay for support than map a format yourself. For most small businesses sending one Comerica file from a clean register, a free browser tool does the same job without a subscription.

Always verify the first file

Whatever you use to build it, test your first Comerica positive pay file with the bank before you rely on it. Send a single file, confirm Comerica accepts it and that the checks match correctly, and only then make it part of your routine. A layout that looks right can still fail on a date format or a field width, and the cheapest place to find that out is the first upload, not the day a fraudulent check slips through. You can also run your file through the format validator first to catch obvious structural problems before you send it.

Create your positive pay file