How this calculator works
Every message carries a fixed cost whether or not you answer it. Reading dominates when most mail is informational; replying dominates when most of it needs a considered answer. The calculator multiplies the daily inbox by the average reading time, then adds the share of messages you reply to multiplied by the time one reply takes. Multiplying that daily figure by five gives the working week, and by the number of working days gives the year. Replies are assumed to be written in the same sitting as the read, which matches the common habit of clearing the inbox in blocks.
Formula
time per day = emails received per day x (time to read one + share replied to x time to write one reply). Time per week = time per day x 5. Time per year = time per day x working days per year. Share of an 8 hour day = time per day / 28,800 s.
Worked example
Forty emails a day at 1 minute each is 40 minutes of reading. Replying to 25% of them at 3 minutes each adds 10 x 3 = 30 minutes, so email takes 70 minutes a working day, about 5.83 hours a week and 303 hours in a 260 day year, or 14.6% of an 8 hour day.
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Frequently asked questions
Does this include time spent switching to email?
No. The figure covers reading and writing only. Context switching after an interruption usually adds more than the message itself, so treat this as a floor rather than a full accounting.
What counts as a reply?
Any message you send in response, including a one line acknowledgement. Set the share to 100% if you answer everything and to 0% for a purely informational inbox.
How do I reduce the number of emails received?
The habits that help are unsubscribing from digests, moving group discussions to a shared document, and setting a schedule for checking the inbox so messages are handled in blocks rather than one at a time.
Why is the year based on working days rather than 365?
Email is a work activity, so weekend and vacation days are excluded. Lower the working days figure to reflect the vacation and holidays you actually take.