Which lens should I buy after the kit lens?

Working out what your kit lens stops you doing, why a cheap fast prime is the usual answer, and reading the numbers on a lens.

Difficulty: beginner
Time: 25 min
Read: 3 min

Short answer

Look at the focal lengths you already use most and what your kit lens cannot do. For most people the answer is a cheap fast prime — a 35mm or 50mm at f/1.8 — which gives low-light ability and background separation the kit zoom cannot.

The kit zoom is competent and limited in a specific way: it is slow, meaning its maximum aperture is small, which costs you low light performance and background blur. That is the gap a second lens usually fills.

Step by step

Look at what you already shoot.Most editing software shows the focal lengths you use most. If almost everything is at the wide end, a wide prime makes sense; if at the long end, you want more reach.
Identify what the kit lens stops you doing.Usually one of three things: it is too dark indoors, the background will not blur, or it does not reach far enough. Each points to a different lens.
Read the numbers on the lens.Focal length in millimetres, and maximum aperture as an f-number. A smaller f-number is a wider opening and more light. A variable figure like f/3.5-5.6 means the aperture narrows as you zoom in.
Account for the crop factor.On APS-C, multiply the focal length by about 1.5 to get the full-frame equivalent, so a 35mm behaves like a 50mm. Micro Four Thirds doubles. Recommendations online often assume full frame.
Consider a fast prime first.A 50mm f/1.8 is usually the cheapest lens in any system and by a wide margin the biggest single upgrade in low light and background separation.
Consider a telephoto zoom for reach.If your subject is sport, wildlife or children at a distance, a 70-200 or 55-250 class lens is the gap. Check what maximum aperture you can afford — cheap long zooms are dark.
Consider a wide zoom for landscape and interiors.Something like 10-20mm on APS-C. It matters far more for property and architecture than for general photography.
Weigh optical stabilisation.Worth having on long lenses and for handheld video; less important on wide primes, and pointless for freezing a moving subject.
Buy used where sensible.Lenses are mechanically simple and hold value. A used copy in good condition from a dealer is close to as good as new at a substantial saving.
Check the weight and size honestly.The best lens is the one you carry. A large fast zoom that stays at home is worth less than a small prime in your pocket.

Tips

A cheap 50mm f/1.8 is the biggest single upgrade most beginners can make.
Multiply by the crop factor before comparing focal lengths with online advice.
Buy lenses used. They are simple, durable and hold their value.

Common mistakes

Buying a superzoom to cover everything — An 18-200 class lens trades optical quality and maximum aperture for range. It is convenient for travel and it will not fix the low-light and background-blur limits that made you want a new lens.
Ignoring crop factor when following recommendations — A 50mm on APS-C frames like a 75mm, which is noticeably tighter than the 'standard' view most advice assumes, and it makes indoor shooting awkward.

If it doesn't work

Indoor photos still dark and blurred

Cause: Slow kit zoom — Fix: A fast prime at f/1.8 gives roughly three stops more light than a kit zoom at its long end.

Background will not blur

Cause: Narrow maximum aperture and short focal length — Fix: A longer focal length at a wider aperture, with more distance between subject and background.

New lens feels too tight indoors

Cause: Crop factor not accounted for — Fix: On APS-C choose 35mm rather than 50mm for a standard field of view.

Questions people ask

Prime or zoom?

A prime for image quality, low light and cost; a zoom for flexibility. As a second lens a prime usually teaches more and adds a capability, where a second zoom often overlaps what you have.

Are third-party lenses any good?

Frequently yes, and often cheaper. Check reviews for the specific mount, since optical and autofocus performance can vary between versions of the same lens.