How Long Will Your Presentation Actually Run?

Presentations overrun because slides get counted and speaking rate doesn't. Here's the conversion, and what it says you need to cut.

Slides get counted; words take the time

Two slides can hold thirty seconds and five minutes of talking. So a slide count tells you almost nothing about how long a talk runs.

What sets the length is speaking rate, and presentation delivery typically runs about 100 to 150 words per minute — slower than conversation, because you're pausing for emphasis and letting an audience read.

A 15-minute slot with 5 minutes of Q&A:


Speaking time	10 minutes
At 130 wpm	1,300 words
A 1,600-word script	12.3 minutes — 2.3 over
Words to cut	300

That last number is the useful one. "Cut some" is an intention. "Cut 300 words" is a decision about which section goes.

Your details

Your slot(min)

Q&A within the slot(min)

Subtracted first — it is not optional time.

Words in your script(words)

Your speaking rate(wpm)

Presentation delivery is typically 100-150. Time yourself out loud.

Slides(slides)

Result

Your talk runs (minutes)

12.3

At your speaking rate, before questions. Minutes, not hours.

Speaking time availableYour slot minus Q&A.: 10
Over or under byPositive means you are over.: 2.3
Words to cutA specific number, not a vague intention.: 300
Words the slot allowsWrite to this figure from the start.: 1,300
Minutes per slideUnder about half a minute means too many slides.: 1

Open the Presentation Timing Calculator on its own page to bookmark or share it.

Subtract Q&A first

It's the first thing forgotten and it isn't optional time.

A 20-minute slot with 5 minutes of questions is a 15-minute talk. Plan 20 minutes of content into it and you'll be cut off mid-conclusion — which is the worst available place to be stopped, because the conclusion is the part people actually remember.

Subtracting it up front means every other number is about time you really have.

Nerves make you faster

This is the one people get backwards, and it matters for how you build margin.

Under pressure most speakers accelerate. A talk rehearsed at a comfortable pace tends to come in short on the day, not long.

That doesn't make a tight talk safe. Talks still overrun — but the overrun comes from a question mid-way, a technical problem, an unplanned aside, or the setup eating your first two minutes. Build margin for those, not for slowing down.

Rehearse out loud, or the timing is fiction

Reading in your head runs far faster than speaking. A silent read-through will always tell you the talk fits, and it will always be wrong.

Time yourself reading your own script aloud, standing up, once. It takes the length of the talk and it replaces every estimate here with your actual rate — which is worth more than any general figure, because the range exists precisely because people differ.

Rehearse the conclusion separately, too. It's the part that gets rushed when you're aware of the clock, and it's the part that shouldn't be.

The minutes-per-slide check

Under about half a minute per slide means you have too many for the time.

Not because of a rule. Because a slide on screen for twenty seconds can't be read and listened to at the same time, so it's doing no work — the audience either reads it and stops hearing you, or hears you and never reads it.

It's a sanity check rather than a target. One slide held for eight minutes is fine if it's the thing being discussed, and a fast sequence of images can be entirely deliberate. Use the figure to catch the accidental version, where a deck grew slide by slide and nobody checked the total.

Decide the drop section before you need it

If you're running late you will cut something, under pressure, and the default is whatever comes last. Which is the conclusion.

So choose in advance: one named section that can go, ideally somewhere in the middle, that the rest of the talk doesn't depend on. Mark it on your notes.

That way the cut you make at minute twelve is the one you'd have chosen calmly at your desk — rather than the one the clock chooses for you.

Count the things that aren't talking

The script isn't the whole talk, and the extras are consistently underestimated.

Slide transitions, waiting for a video to load, a demo that needs a moment, walking to the screen, the pause while someone at the back asks you to go back a slide — none of it is in your word count, and together it's routinely a minute or two.

Check whether your slot includes setup. If you have fifteen minutes from the moment the previous speaker sits down, connecting a laptop and finding the right window is coming out of your talk. That's a common way to lose the first ninety seconds of a fifteen-minute slot, and it's entirely avoidable by asking beforehand.

Write to the word budget from the start

The most useful direction to run this is backwards.

Work out the budget first — speaking minutes multiplied by your rate — and write the script to that figure. A 10-minute talk at 130 words a minute is a 1,300-word script, and knowing that before you write is much cheaper than discovering it after.

Writing first and cutting later is how the conclusion ends up compressed, because it's written last against a budget that's already gone. Same failure mode as an essay, for the same reason.

Practise the version you'll actually give

One rehearsal, out loud, standing, timed, with the slides advancing.

Not reading at your desk. The seated silent version is a different activity that takes a different amount of time, and it's the one that tells you everything fits.