How to plan the timing for layout?

Question

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Actually a question.
I tried to plan everything block by block - layout of the header: 2 hours, layout of the catalog: 3 hours.
But then, when you start working directly, it turns out that it takes 4 hours for the header, and all 6 for the catalog.
Moreover, when you just plan, the deadlines seem quite real, you even throw them a little over (I make it up in an hour and a little, but I’ll write 2). Convince yourself to write 4 hours at once, if an hour or more is internally planned, conscience does not allow - the customer / manager will tell you why it takes so long or completely abandon the project.
On the scale of the monthly project, there are discrepancies up to one and a half times, which, of course, does not please anyone.
I have enough experience in layout, but it’s hard to plan the deadlines correctly — towards the end of the project, sleepless nights begin in order to meet the deadline.
Many are faced with this, share the secret of how to meet deadlines, not overestimate them, sleep at night and work with a cheerful attitude.

Answer 1

This is normal, all people have such a systematic mistake - to underestimate the deadlines. Stupidly we are so arranged. An experienced manager/customer usually knows what this ratio is.
If you know for yourself that on average you have a mistake twice, well, throw it right away. From experience, I can say that it is more important for a business to do it in two weeks, than to promise in a week and delay it for two.

Answer 2

Estimate, multiply the time by 2 and you get real terms.
Well, either use the formula from Bobuk )