Does anyone actually plan annual nitrogen totals, or am I overthinking lawn care?

I live in NZ and am pretty obsessive about lawn care and realised I was constantly doing mental maths (or messy notes) around fertiliser rates, nitrogen targets, and timing through the year.

I’ve used all the usual calculators, but they’re mostly “one application at a time”. I started building a spreadsheet that:

– plans fertiliser applications across a full year

– tracks cumulative nitrogen so you don’t accidentally overdo it

– works with any fertiliser (just enter N‑P‑K), not brand‑specific

– isn’t tied to US-only assumptions

Before I go too far with it — curious how others handle this.

Do you:

– actually track annual nitrogen / nutrients?

– use your own spreadsheet?

– just follow a program and not worry about totals?

I am genuinely interested how people here approach it.

Also added a photo of my back lawn so it isn’t just a wall of text!