How many photos does a time-lapse need?

The arithmetic is one line:

photos = video length in seconds × frames per second

Everything else is judgement about which frame rate suits a slow subject, and how many frames you actually need before the thing starts to work.

What is the minimum number of photos?

About 30 frames.

Below that, the eye tracks each photo individually. You watch a sequence of stills, register each one, and the effect is a slideshow no matter how fast it plays. Above roughly 30, perception flips: you stop seeing photos and start seeing the change between them. That flip is the entire reason to make a time-lapse rather than a before and after.

Thirty frames is not a hard threshold, and busy subjects like a room being rebuilt can work with fewer because each frame carries more difference. A face changes so little per frame that it wants more. But 30 is the number to plan around.

What a frame count actually buys you

12Reads as a slideshow. Show it as a before and after instead.

30The floor. The eye starts tracking change rather than photos.

120Ten seconds at 12fps. Plenty, and probably worth trimming.

How long does each cadence take to get there?

This is the part that decides whether a project is realistic.

Cadence	30 frames	60 frames	120 frames
Daily	1 month	2 months	4 months
Every other day	2 months	4 months	8 months
Twice a week	15 weeks	7 months	14 months
Weekly	7 months	14 months	2.3 years
Every two weeks	14 months	2.3 years	4.6 years
Monthly	2.5 years	5 years	10 years

The row that surprises people is weekly. A weekly gym project does not produce a watchable time-lapse for around seven months. That is not a flaw in the plan, it is just the honest timeline, and knowing it up front is what stops people abandoning the project at week six because “there is nothing to show yet”.

If you want the video sooner, the options are to shoot more often, which only works if the subject genuinely changes that fast, or to lower the frame rate.

Which frame rate suits progress photos?

Between 8 and 15 frames per second, and 12 is a good default.

That is much lower than the 24 or 30 frames per second used for motion video, and deliberately so. Video frame rates exist to make continuous motion look smooth. A progress time-lapse is not continuous motion, it is a series of discrete states, and each state needs a moment on screen to register.

Frame rate	30 photos	60 photos	120 photos	Feel
6 fps	5.0 s	10.0 s	20.0 s	Slideshow, each frame lands hard
8 fps	3.8 s	7.5 s	15.0 s	Deliberate, good for faces
12 fps	2.5 s	5.0 s	10.0 s	The general default
15 fps	2.0 s	4.0 s	8.0 s	Brisk, good for busy subjects
24 fps	1.3 s	2.5 s	5.0 s	Too fast for most progress work

The trade is straightforward. A lower frame rate stretches a small number of photos into a longer video, at the cost of feeling stepped. A higher one feels smoother and burns your material faster. When a project is young, favour the low end.

How long should the finished video be?

Between 5 and 15 seconds for anything going onto a vertical feed.

Progress time-lapses are repetitive by nature, which is their charm for the first few seconds and their problem after that. The change is roughly linear, so the twelfth second contains no new kind of information, only more of the same. Attention drops accordingly.

If you have 300 photos, that does not mean you should show all 300. Consider trimming to the stretch where the most change happened, or raising the frame rate so the whole run fits in ten seconds.

Does missing days ruin it?

Almost never.

A time-lapse is robust to gaps in a way people do not expect. A missing day in a 90 frame sequence is one thirtieth of a second of slightly larger jump, and viewers do not perceive it. Two missing weeks in a weekly project is more visible, but still reads as a slightly faster stretch rather than as an error.

What does damage a sequence is a framing gap: a photo taken from a different spot sits in the middle of the run as a jolt, and the eye catches it instantly. One badly framed frame is more disruptive than five missing ones.

Which produces a useful rule for the days when you cannot be bothered: if you cannot take the photo properly, skip it. A missing frame costs almost nothing. A misaligned frame costs more than it adds.

Working the numbers for your own project

The time-lapse calculator runs this in both directions: forwards from a routine you already have, and backwards from a video length you want. It also flags the case people most often walk into, which is a target video length that quietly implies four years of shooting.