Bana kalırsa bu plan iyi.

In natural English, bana kalırsa means in my opinion, as far as I’m concerned, or if you ask me.

Literally, it comes from something like if it were left to me or if it remained up to me, but in everyday Turkish it is just a common way to give your opinion.

So:

Bana kalırsa bu plan iyi.
= In my opinion, this plan is good.

Because bana is the dative form of ben.

• ben = I
• bana = to me

The expression bana kalırsa uses bana, not ben, because the idea is roughly if it is left to me / according to me.

This is very common in Turkish: after some verbs and expressions, you need a case ending, not the plain dictionary form of the pronoun.

Kalırsa comes from the verb kalmak, which usually means to stay, to remain, or sometimes to be left.

Here it breaks down like this:

• kal- = verb stem
• -ır = aorist / general-habitual marker
• -sa = conditional if

So kalırsa is roughly if it remains / if it is left.

In bana kalırsa, though, the whole phrase works idiomatically, so you should learn it as a set expression meaning in my opinion rather than trying to translate every piece every time.

Yes, it is basically an idiomatic expression.

A word-for-word interpretation can help you understand where it comes from, but in real use you should treat bana kalırsa as a fixed phrase for giving an opinion.

Similar English expressions are:

• in my opinion
• if you ask me
• personally

So if you try to interpret it too literally every time, it may feel confusing. It is better to recognize it as a standard opinion phrase.

Because in present-tense Turkish, the verb to be is often not expressed in simple sentences like this.

So:

• bu plan iyi = this plan is good

Turkish very often uses this kind of zero copula in the present tense.

Compare:

• Bu plan iyi. = This plan is good.
• Hava güzel. = The weather is nice.
• Ben yorgunum. = I am tired.
  (Here a personal ending appears because the subject is a person.)

So there is no missing word in the Turkish sentence; this is just how Turkish normally works.

Because these two forms do different jobs.

• bu plan iyi = this plan is good
  This is a full sentence.

• iyi bir plan = a good plan
  This is just a noun phrase, not a complete sentence by itself.

If you want a full sentence with iyi bir plan, you would say:

• Bu iyi bir plan. = This is a good plan.

So:

• Bu plan iyi. focuses on the plan is good
• Bu iyi bir plan. means this is a good plan

Both are correct, but they are structured differently.

Yes, Turkish word order is flexible, but the usual neutral order here is:

Bana kalırsa bu plan iyi.

This sounds natural and straightforward: first the opinion phrase, then the statement.

You may also hear variations such as:

• Bu plan, bana kalırsa, iyi.
• Bu plan iyi, bana kalırsa.

These can change the emphasis slightly, but the basic meaning stays the same.

For a learner, Bana kalırsa bu plan iyi is a very good standard version to use.

Yes. Bence is one of the most common alternatives.

• Bence bu plan iyi. = I think this plan is good / In my opinion, this plan is good.
• Bana kalırsa bu plan iyi. = In my opinion, this plan is good.

The difference is mostly one of style and nuance:

• bence is very common, short, and direct
• bana kalırsa is a bit more expressive, like if you ask me

Both are natural. As a learner, it is useful to know both.

Yes. Bu means this.

So:

• bu plan = this plan

Turkish does not use articles like a and the the same way English does, so bu is not an article—it is a demonstrative.

Compare:

• plan = plan / a plan / the plan depending on context
• bu plan = this plan
• şu plan = that plan (often something a bit more specifically pointed out)
• o plan = that plan

You would usually negate the adjective part:

• Bana kalırsa bu plan iyi değil.
  = In my opinion, this plan is not good.

Here:

• iyi = good
• değil = not / is not

So iyi değil means not good.

This is a very useful pattern:

• Bu fikir iyi. = This idea is good.
• Bu fikir iyi değil. = This idea is not good.

It is neutral and natural. You can use it in everyday speech and in normal writing.

• bence may sound a bit more casual and conversational because it is shorter.
• bana kalırsa is still very normal, but can feel slightly more thoughtful or emphatic.

So Bana kalırsa bu plan iyi is perfectly fine in most ordinary situations.