Per pane sounds fair and is a trap. It rewards the customer with forty tiny Georgian panes and punishes the one with two big sheets of glass, when the second house is quicker, easier and better for your back. Counting panes also takes time at the quote, and it invites an argument about whether a fanlight counts.
Per property is what most established rounds run on, and the number should come from time, not from sympathy. Work out what you need to clear per hour after fuel, resin, insurance and the van, then estimate the job honestly including setting up and packing down. A twenty minute job at a rate of forty an hour is not a fifteen pound job.
Density beats rate
The thing that actually decides your income is density. Ten houses in one street at fifteen pounds beats six houses across three villages at twenty five. Every mile between jobs is unpaid, and a scattered round quietly eats a day a week. When you are starting out, take the cheap job next door to the good one and refuse the good one twelve miles away.
Raise prices on the round you have rather than chasing new work at the old rate. A pound a house across two hundred houses on a four weekly cycle is meaningful money and almost nobody cancels over it. The ones who do were the ones ringing about spots after rain.
First cleans should cost more and almost never do. The first visit to a house that has not been touched in two years takes twice as long, and if you price it as a regular clean you have trained the customer to expect that rate forever. ▪