Electrical – How to pick voltage rating for capacitors

This page has the following table:

So, if the 22uF is a 20% tolerance part such that is may actually be 17.6uF (-20%), and it is really 15uF (-15%) due to heating, it may be reduced to ~10.5uF (-30%) near its tolerance or ~14uF (-5%) near its operating point. To reduce the effect, use a higher breakdown value capacitor.

Although this webpage tests much higher breakdown voltage ceramics, the results are illustrative:

This part, the 08056D226MAT2A by AVX, states that it meets its tolerance tested at 0.5 V_RMS, not close to its breakdown:

For Cap > 10 μF, 0.5Vrms @ 120Hz

It also mentions that capacitance may change up to 12.5% over its load life, 7.5% due to soldering thermal shock, and 12% due to flexure fissures (cracks).

_{Info tidbit: The term X5R means it is composed of a class 2 dielectric (ie: ceramic) that will maintain its capacitance to within 15% (18.7uF - 25.3uF) over a temperature range -55^oC to 85^oC.}
Something that may interest you, though it has more to do with the final application than the question -- the great 'pedia also mentions:

Due to its piezoelectric properties, they are subject to microphonics.

... And the previously linked page:

High-K ceramic capacitors can show significant piezoelectric effects; if you tap them they will produce a voltage spike. This is caused by the barium titanate, the main material in high K ceramics. The higher the K, the stronger this affect.

Some cap vendors make their own parts. Some buy caps from a smaller manufacture with the reels re-branded at the fab. Watch out. I got into a mlcc failure investigation in 2002 and started inspecting caps on a reel under a microscope. 3/10 came off the reel cracked. A crack will sooner or later lead to a short. Cracks are not obvious even under a microscope. They may present as a subtle colour shift if the crack is below the surface layer. Some cracks may be sufficient to present a short immediately. Not all. The vendor's manufacturer in this case eventually identified a hopper where the caps were getting cracked.

MLCC are very sensitive to mechanical stress. Especially bigger than 1210 sizes. I found a big power bypass cap adjacent to a heavy mechanical connector once. The nearest mounting hole was 2" away! They were cracking at a rate of 5/10 during install of the unit. A fraction of those were catching fire. The fire would continue to burn until it melted the copper, breaking the power connection.

Another effect of a crack is a reduction of the max working voltage of the cap. It might be spec'd for 200 V. But once cracked it may break down at 40 V. Cracked caps burst into flames in my lab when tested - even below their rated voltage.

Another way to warm up caps is exceeding their max ac current. It's easy to think of caps as zero power dissipation devices. Especially the higher Q mlcc. But they're not. Calculate the power dissipated in caps and do not exceed power/ac current limits. Shows up in power circuits and converters commonly.