Le tarif change lorsque l’estimation est rectifiée.

Because tarif is a masculine noun in French, so it takes le in the singular.

• le tarif = the rate / the fee / the pricing
• un tarif = a rate / a fee

This is something you usually just have to learn with the noun.

Because estimation begins with a vowel sound, and French normally drops the vowel of le or la before a vowel or mute h.

So:

• la estimation → l’estimation

This is called elision. It happens very often in French:

• l’hôtel
• l’idée
• l’entreprise

Change is the present tense of the verb changer.

Here it is the 3rd person singular, because the subject is le tarif:

• je change
• tu changes
• il / elle / on change
• le tarif change

So in this sentence, change means changes.

Not exactly.

French change is pronounced roughly like shahnzh, not like the English chaynj.

A few important differences:

• the first sound is sh as in shoe
• the an is a nasal vowel
• the final g is soft, like the s in measure

So it sounds much more French than the English word, even though the spelling looks familiar.

French often uses the present tense to express:

• a general truth
• a rule
• a habitual action
• how a system works

So Le tarif change lorsque l’estimation est rectifiée means something like a general rule: whenever that correction happens, the rate changes.

English often does the same:

• The price changes when the estimate is corrected.

Lorsque is a conjunction meaning when.

In many situations, lorsque and quand can both mean when. The main difference is usually register:

• quand is more common in everyday speech
• lorsque sounds a bit more formal or written

So this sentence sounds slightly formal or administrative, which fits words like tarif and estimation.

Because this part is in the passive voice.

Est rectifiée = is corrected / is revised

It is formed with:

• être in the present tense: est
• a past participle: rectifiée

So:

• l’estimation est rectifiée = the estimate is corrected

An active version would be something like:

• On rectifie l’estimation.
• Quelqu’un rectifie l’estimation.

The passive is common in formal, technical, or administrative French because it focuses on the thing affected, not on who does the action.

Because the past participle agrees with l’estimation, which is:

• feminine
• singular

With être in the passive, the past participle agrees with the subject.

So:

• masculine singular: rectifié
• feminine singular: rectifiée
• masculine plural: rectifiés
• feminine plural: rectifiées

Since estimation is feminine singular, we get rectifiée.

Here it takes the indicative, not the subjunctive.

That is why we have:

• lorsque l’estimation est rectifiée

The sentence describes a real event or a normal rule, so the indicative is the natural choice.

In general, lorsque usually introduces something seen as real, factual, or expected, so the indicative is most common.

They are related, but not exactly the same.

• prix = price in a broad sense
• tarif = rate, charge, fee, pricing schedule, or set price in a system

So tarif often sounds more appropriate for:

• services
• fees
• official pricing
• transport
• insurance
• utilities
• administrative or business contexts

That is why tarif works well in a sentence that sounds formal or procedural.

Yes, grammatically you could say:

• Le tarif change quand l’estimation est rectifiée.

That would still be correct.

The version with lorsque simply sounds a bit more formal and polished. In business, legal, technical, or website language, lorsque is often preferred.