Invoice with hourly rates plus lump sum / fixed rate
I bill my clients per time plus when I work for them at their location I charge a fixed rate that covers the time and expenses spent on travelling to them. When I work from my office, I do not charge them that fixed rate of course but only the time that I worked for them.
My question is: How to include the fixed rate for travelling in my invoices?
Currently I am using Google Sheets to keep track of my work and have a column to state if the fixed rate applies. Ideally, I had hope for a checkbox like that in Zoho Invoice. But maybe I am missing another convenient way to include my fixed rates in my invoice.
Thank you for your suggestions!