Yağmur yağınca ben gün boyu evde kalıyorum.

-ınca / -ince / -unca / -ünce is a common Turkish verb ending meaning when, once, as soon as, or sometimes whenever, depending on context.

So:

• yağmak = to rain
• yağınca = when it rains / when it starts raining / whenever it rains

In this sentence, it connects the first action to the second one:

• Yağmur yağınca → When it rains
• ben gün boyu evde kalıyorum → I stay at home all day

The exact shade in English depends on context, but when/whenever it rains is a very natural understanding here.

This is very normal in Turkish.

• yağmur = rain
• yağmak = to rain / to fall (for rain, snow, etc.)

So yağmur yağmak literally looks like rain rains, but that is just how Turkish commonly expresses the idea it rains.

Similar patterns happen with other weather expressions:

• kar yağıyor = it is snowing
• yağmur yağıyor = it is raining

So yağmur yağınca simply means when it rains.

This is a very common learner question, because Turkish uses the present continuous more broadly than English does.

• kalıyorum literally looks like I am staying
• but in everyday Turkish it can also mean a habitual or regular action, especially when the context makes that clear

So here, Yağmur yağınca ben gün boyu evde kalıyorum can naturally mean:

• When it rains, I stay home all day
• Whenever it rains, I stay at home all day

If you said kalırım, that would also be possible in some contexts and can sound more like a general rule or tendency:

• Yağmur yağınca evde kalırım = When it rains, I stay home / I tend to stay home

But kalıyorum is very natural in spoken Turkish for repeated real-life situations.

Both can often be translated as when it rains, but there is a nuance.

• yağınca often feels a bit more like:

  • when it rains
  • once it starts raining
  • whenever it rains

• yağdığında is also when it rains / when it is raining, but it can sound a little more neutral, descriptive, or time-specific.

Very roughly:

• Yağmur yağınca evde kalıyorum.
  = When(ever) it rains, I stay home.

• Yağmur yağdığında evde kalıyorum.
  = When it is raining, I stay home.

In many everyday situations, the difference is small, but -ınca is especially common for this kind of cause/time relationship.

No, ben is not necessary.

Turkish verbs already show the subject:

• kalıyorum = I stay / I am staying

So the sentence could simply be:

• Yağmur yağınca gün boyu evde kalıyorum.

That is often the more neutral version.

Adding ben can give:

• emphasis
• contrast
• clarity

For example, you might say ben if you are contrasting yourself with someone else:

• Yağmur yağınca ben evde kalıyorum, kardeşim dışarı çıkıyor.
  = When it rains, I stay home, but my sibling goes out.

So ben is optional, not wrong.

gün boyu means all day or throughout the day.

It is made from:

• gün = day
• boyu = along the length of / throughout

So gün boyu gives the idea of the whole span of the day.

Examples:

• Bütün gün = all day
• Gün boyu = all day / throughout the day

These are often similar in meaning, though gün boyu can feel a little more like through the whole course of the day.

Because kalmak usually takes the location where you stay, not the destination you go to.

• evde = at home / in the house
  (-de = in/at/on, the locative case)

• eve = to the house / homeward
  (-e = to, the dative case)

So:

• evde kalmak = to stay at home
• eve gitmek = to go home

In this sentence, the idea is not movement toward home, but remaining there, so evde is correct.

The word order is natural, but Turkish word order is flexible.

This sentence is:

• Yağmur yağınca = when it rains
• ben = I
• gün boyu = all day
• evde = at home
• kalıyorum = I stay

A very typical Turkish pattern is to put the main verb at the end, and other information before it.

So this order sounds natural:

• Yağmur yağınca ben gün boyu evde kalıyorum.

But some parts can move for emphasis:

• Ben yağmur yağınca gün boyu evde kalıyorum.
• Yağmur yağınca evde kalıyorum gün boyu.
  (possible, but less neutral)

The most neutral and standard thing is still to keep kalıyorum at the end.

It can overlap with all of those in English, but the most natural meaning here is usually:

• when it rains
• whenever it rains

That is because the sentence sounds like a repeated habit or typical reaction.

Depending on context, yağınca can sometimes feel close to if/once it starts raining, but here the whole sentence strongly suggests a regular pattern:

• rain happens
• then I stay home all day

So whenever it rains, I stay home all day is a very good interpretation.

It comes from the verb stem plus the -ınca type ending.

• dictionary form: yağmak
• remove -mak → yağ-
• add -ınca → yağınca

The exact form changes by vowel harmony:

• -ınca
• -ince
• -unca
• -ünce

For example:

• gelmek → gelince = when he/she/it comes
• bakmak → bakınca = when he/she/it looks
• oturmak → oturunca = when he/she/it sits down / when he/she/it is seated
• görmek → görünce = when he/she/it sees

So yağınca is just the regular vowel-harmony form for yağmak.

Yes, in the right context, that is possible.

Because yağmak already strongly suggests weather like rain or snow, a speaker might say:

• Yağınca evde kalıyorum.

This would usually be understood as When it rains, I stay home, especially if the context is clear.

However, yağmur yağınca is also very normal and explicit. It makes the sentence clearer and more complete on its own.

So both are possible:

• Yağmur yağınca evde kalıyorum.
• Yağınca evde kalıyorum.

The first is clearer if the sentence stands alone.