How much money can I realistically save by bringing lunch to work instead of spending $7 for cafeteria food?

It is impossible to tell without determining the cost of the food you are bringing to work instead.  If it costs you $7 a day to a make your lunch, you'll save nothing.

I've been wondering the same since I have been doing this for a few months. I usually make myself a nice salad and my colleagues look at it with jealousy... An average meal costs me about 2,50eur. The meal at the canteen costs at least 7eur. With 22 meals per month that's about 100eur saved per month. Sometimes more, sometimes less. One thing I am not considering here is the quantity and the quality. I eat much better. And if I would try to get the same kind of food from the canteen it would cost me a lot more. Probably around 9eur. So that's about 6,50/day and 145/month, 1700 eur/year

Realistically how much you can save is depend on how much you are willing to spend for making lunch. If you are trying to save money, you should make a simple lunch which cost less. For example, if it were me, to save money, i will make a simple sandwich which probably cost around $2 or less (this is just an assumption as i do not know the price for the bread+egg+salad at your place). However, assuming you don't have any intention to save money and just for the sake of making lunch, i doubt that you will save more money than what you are already spent eating on cafeteria.

That's simple math.  Multiply your working days during the year (260) Add the hassle of meal prep.. unless your husband/wife/significant other SHOPS, DICES, CHUNKS and prepares your meals, including salad and fruit for dessert. Add the noisy, unbearable conversation from co-workers and not being able to escape office politics even during lunch. Cash saved (260) x $7.00= $1820.00 $1820, +Hassle: You put the price +Prep work: Engage others, you determine the price.. +Add 3 hrs. shopping to your already crazy week. +Add some healthier eating -Minus all the things mentioned above. Lunch is a necessity, specially if you don't have a healthy breakfast to start with.  AND:  if you want to keep on budget, you'll have to drink water from the water cooler.) x 260 days. Stop your coffee on the way to work $2 - $7 depending on how complex your tastes are. Plus the mid-morning escapade to Starbucks $2- $7.00. Multiply x 260 Take off your vacation days..and business lunches.