Open Perussanakirja and count the headwords containing each letter. Iso suomen kielioppi did, and printed the result: about 1,400 words with an f, about 1,300 with a b, about 1,600 with a g, and about 60 spelled with š.
Then the comparison that makes those numbers mean something. Headwords containing v, or containing p: about twenty thousand each.1

The grammar says it in as many words
This is not an inference from the counts. It is the standard grammar’s own opening sentence on the subject: the sounds f, š, b and g came into the standard language with loanwords, they occur mainly in foreign and slang words, and “their position in the sound system is not as stable as that of the other sounds”.1
Š is described there as the rarest sound in Finnish. It is often written sh or ch instead, which is why shampoo and sampoo are both in circulation.2 Its voiced partner ž is more marginal still, surviving in perhaps a handful of words: džonkki, maharadža.
D belongs with them in foreign and slang vocabulary, which is worth holding onto, because it is also the consonant whose realisation varies most across the country.
| Sound | Headwords in Perussanakirja | Turns up in |
|---|---|---|
| Soundp | Headwords in Perussanakirjaabout 20,000 | Turns up ineverything |
| Soundv | Headwords in Perussanakirjaabout 20,000 | Turns up ineverything |
| Soundg | Headwords in Perussanakirjaabout 1,600 | Turns up ingaala, jogurtti, glögi, diggaa |
| Soundf | Headwords in Perussanakirjaabout 1,400 | Turns up infarkut, katastrofi, futis, safka |
| Soundb | Headwords in Perussanakirjaabout 1,300 | Turns up inbanaani, bussi, biisi, bailaa |
| Soundš | Headwords in Perussanakirjaabout 60 | Turns up inšakki, shampoo, tšekki |
The slang column is not decoration. Helsinki slang is full of these sounds because it is full of Swedish, and the words that carry them - duuni, safka, biisi - never went through the adaptation the older loans did.
What it predicts about your accent
The interesting part is that the rule runs in both directions, and most learners have only noticed one of them.
Into Finnish. Your b and g are probably crisper than the room’s, which costs nothing and is never commented on. What does get noticed is length, and that is a different problem with a different fix.
Out of Finnish. A Finnish accent in English is partly this same sound system running backwards: a borrowed sound is pulled toward its nearest native neighbour, so th arrives as t or s, w as v, z as s, and p, t and k come without the puff of air an English ear is listening for. The clusters are not the problem any more. That happened to the loanwords, not to the speakers.
This is not where pronunciation effort goes. Vowel and consonant length change the word; a slightly foreign b does not. Kielibuusti's own phonetics guide for learners leads with length and with one-letter-one-sound, and does not spend a slide on the borrowed consonants.
Know this instead because it is an explanation rather than a drill. It tells you why the vocabulary looks the way it does, and that is worth more per minute than any amount of repeating banaani.
Why old loans look Finnish and new ones do not
Two rules, both from the grammar, and together they explain a whole class of word shapes.345
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1A native syllable is CV or CVCFinnish syllables are typically a consonant plus a vowel, or a consonant, a vowel and a consonant. Other syllable types "occur in foreign and slang words", where a cluster like str, spr, skr or kl can open a word or a later syllable. Native Finnish word shapes do not do that.
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2The older the loan, the more adapted it isBorrowed words "have generally been adapted to Finnish phoneme and word structure", and the grammar states the consequence plainly: the age of a loan shows in its shape, and the older it is, the more adapted. Three-syllable and longer loans are on average younger and closer to their source word than two-syllable ones.
Put those together and a word’s shape becomes a rough date stamp. A short, cluster-free, b-free, g-free word has usually been in the language long enough to have been filed down. A word that opens with tr or carries a g in the middle arrived recently enough to keep them.
The grammar adds the part that is easy to miss: the loans have not only been changed by Finnish, they have changed Finnish. Syllable types and consonant phonemes that the language did not formerly have are in it now because borrowed words brought them.4

The borrowed layer came mostly from one place: a study applying the Loanword Typology core-meaning list to Finnish found that 69 per cent of the borrowed meanings in its sample came from Swedish or its earlier Germanic stages.6 The sounds arrived with the words, over a very long time and from a very small number of directions.

There is a useful counter-example on any Finnish shoreline. Äkkisyvää, the warning sign meaning sudden deep water, is four consonants and five vowels, and not one of the consonants is borrowed.

So the practical test, if you want one: a Finnish word with a b, a g, an f or a cluster at the front is a word that came from somewhere else, and recently enough that nobody filed it down. That is several thousand words you can date at a glance.
Footnotes
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VISK § 6 Äänteet f, š, b ja g: bluffata, tšekki, jogurtti - Iso suomen kielioppi. Source of the statement that these sounds entered with loanwords, that š is the rarest sound in Finnish, and of the Perussanakirja headword counts ↩
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Kielitoimiston sanakirja: šakki - Institute for the Languages of Finland ↩
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VISK § 11 Tavu kielen rakenneyksikkönä ja suomen tavutyyppejä - Iso suomen kielioppi, on Finnish syllable types and the cluster-initial syllables found in foreign and slang words ↩
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VISK § 150 Lainasanakerrostumat ja lainojen mukautuminen - Iso suomen kielioppi, on the layers of loans, their adaptation, and the effect they have had on Finnish phonotactics ↩
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Phonetics for Finnish learners - Kielibuusti, University of Helsinki ↩
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Quantifying loanwords: a study of borrowability in the Finnish lexicon - Sandra Cronhamn, Lund University ↩











