If I'm connected to Wi-Fi and I download a free app, will it use my data?

If I'm connected to Wi-Fi and I download a free app, will it use my data?

I barely have any data left but I really want this app. If I'm connected to Wi-Fi and I download it, will it use my data? I have an iPhone 4 by the way, if that changes anything.

It shouldn't but if you want to be sure turn off data while you are downloading it.

Settings > General > Cellular > Cellular Data Off

You will download it via Wi-Fi. Now it might use data elsewhere.