I spend money literally every single day — is a no-spend day a real thing or is it budget theatre?

Disagreeing with the whole framing, politely. £180 a month is real money, but it is a rounding error next to the three numbers that actually decide your savings rate: what you pay for housing, what you pay for a car if you have one, and what you earn. I spent two years optimising small spending and moved my savings rate by a couple of points; I moved it by fifteen points in one afternoon by changing where I lived when the lease came up. Do the small stuff if it is fun, but do not mistake it for the lever.

Spending most days is completely normal and not by itself a symptom of anything. The question worth asking is not whether you spent, it is whether you can name what you bought a week later. Anything you cannot name is the part to look at.

I did no-spend days for a year and the money saved was almost irrelevant next to what it taught me. About a third of my small transactions were not for a thing I wanted, they were for a moment of friction — bored on a walk, tired at the station, avoiding going home. Once I could see the pattern I could deal with the actual cause, and the spending fell away as a side effect. The honest number for me was around £60 a month, not the full £180, because plenty of it just moved to other days.

The thing that worked for me was not a rule but a delay. Anything under a tenner that I wanted while out went on a note in my phone, and I bought it on Saturday if I still wanted it. Roughly two thirds of the list never got bought and I never once felt deprived, because I had not said no, I had said later.

Weekly cash for discretionary spending, one withdrawal, and when it is gone it is gone. Crude, effective, and it works precisely because a card makes every small amount feel like the same amount.

Categorise before you judge. My daily spending looked awful until I split it into food I would otherwise have cooked, transport I could not avoid, and genuine impulse. The impulse portion was about a quarter of the total. The rest was not a discipline problem, it was that I had no lunches in the house, which is a shopping problem with a completely different fix.