How much room a business card actually gives you
Card real estate is tiny, and the QR code is almost always fighting for space on the back of the card while your name, title, and logo hold the front. As a working minimum, keep the printed code at least 1.5-2cm square — smaller than that and you're relying on a phone camera to resolve modules that are barely bigger than the paper fibers around them, especially under normal indoor lighting.
Leave a clear quiet zone (blank margin) around the code rather than butting it against a border line or the edge of the card — that margin is what tells a scanner where the pattern starts and stops. If you're not sure a size will scan, print a single test card at actual size and scan it with two or three different phones before sending the full batch to print.
Foil, spot color, and gradient prints
Solid black on white (or a single dark spot color on a light background) scans more reliably than anything fancier, and at business-card size that reliability matters more than the aesthetic upgrade. Foil stamping looks premium, but foil is reflective — under the wrong light angle it can wash out the contrast a scanner needs, so if you're set on foil, test the actual foil-and-paper combination before committing to a print run.
Gradient or multi-color QR styles are best avoided on a card this small. They can look sharp in a design mockup, but a gradient reduces the contrast between adjacent modules right when you need every bit of contrast you can get — stick to a single solid, dark color for the code itself, and save the gradient for the rest of the card design.
What to actually link to
The whole point of a business card is "save my info," so a vCard or contact-download link often serves that better than a homepage link — one scan and you're already in their contacts app, no typing required. That said, the right destination depends on the role: a real estate agent might link to a current listing or booking page, a salesperson to a LinkedIn profile or calendar link, a consultant to a booking page, and a contractor to a gallery of past work or a reviews page.
If you specifically want to send people to a portfolio, case study, or resume, QRSen has a dedicated page with advice for that exact use case — this page is about business cards in general, for any profession, and any destination that gets someone from "I have your card" to "I've taken the next step."