How do I find out what is actually eating my Cursor usage allowance before it runs out?

Yes to the second one, and it is the answer to your whole question. Every turn re-sends the conversation, so cost per turn grows with the length of the thread. Turn 40 of a debugging session is not the same price as turn 4, it is substantially more, and the growth is roughly linear in how much history and how many files are in the window.

Practical consequence: start new chats aggressively. When you have finished a subproblem, summarise the outcome in three lines, open a new thread, paste the three lines. I halved my spend doing only that, without changing model.

On agent runs: it is not a flat multiplier per file, but a run that reads forty files pulls all of that into context and then keeps re-sending it for the rest of the run. The expensive thing is the reading, not the editing.

Build the ledger yourself, because the vendor total will never tell you which task it was. One row per task: date, what it was, which model I picked, how many turns, did it land without a rewrite. Five seconds per row.

After two weeks you can sort by "cost per thing that actually shipped" and the answer is usually embarrassing and specific, like one category of task consuming a third of the allowance while producing work I threw away. That is a decision you can act on. A monthly total is not.

Before building anything, look at the usage page in your account. There is a running view of what has been consumed and by which model, which is enough to answer "is it the fast variant" and "is it one model or all of them" without instrumenting anything. Check it on a Monday and again on a Wednesday and you will have a burn rate.

The biggest single lever in my experience is standard versus fast variant, because it is a several times multiplier that you set once and then forget you set.

One structural thing that helps if you are also paying for API calls elsewhere: cached input is discounted on several providers. xAI publishes a 75% discount on cache hits for Grok 4.5, for instance. That only pays off if the stable part of your prompt is at the front and byte identical between calls, so putting your long system context first and the varying part last is free money on repeated calls.

Check whether the specific thing you are paying for exposes caching at all before restructuring anything. Inside an editor you often do not control it.

Blunt possibility worth entertaining: if you are hitting the limit on day nine consistently, the honest conclusion might be that your workload costs more than $20 a month and no amount of attribution changes that. Measure for two weeks, then decide whether you are optimising a real inefficiency or just rationing something you should be buying more of.