Learn Hardcore German: Mein Gewicht ist heute das gleiche wie gestern. - My weight is the same today as yesterday.

The noun Gewicht is understood and not repeated, which is why gleiche is “turned into a noun” (nominalized) and gets capitalized in some other contexts (e.g. das Gleiche when standing alone). In this exact sentence, many would still write das gleiche lowercased because it’s seen as a regular adjective phrase referring to Gewicht. You will see variation in real life. Learners are usually taught das Gleiche (capital G) when it stands for “the same thing.”

Why do we use wie instead of als in this comparison?

German distinguishes:

For equality: use wie
- so groß wie = as tall as
- genauso schwer wie = just as heavy as
- das gleiche wie = the same as
For inequality: use als
- größer als = bigger than
- schwerer als = heavier than

In the sentence

Mein Gewicht ist heute das gleiche wie gestern.

we are saying the weight is equal to yesterday’s weight, so wie is the only correct choice.
✗ Mein Gewicht ist heute das gleiche als gestern is wrong.

Could I say Mein Gewicht ist heute gleich wie gestern instead? What’s the difference?

You can hear and read:

Mein Gewicht ist heute gleich wie gestern.

but there are some nuances:

Standard German / textbook style favors:
- Mein Gewicht ist heute dasselbe wie gestern.
- Mein Gewicht ist heute das gleiche wie gestern.
- Mein Gewicht ist heute so hoch wie gestern.
Gleich wie is somewhat regional (very common in Austria and parts of southern Germany). In strict standard German, people often prefer structures with so … wie or das gleiche / dasselbe … wie rather than just gleich wie.

So your sentence with gleich wie will be understood and sounds natural in many regions, but for exams or very standard writing, stick to:

Mein Gewicht ist heute das gleiche wie gestern.
Mein Gewicht ist heute dasselbe wie gestern.

What’s the difference between das gleiche and dasselbe here?

There is a theoretical distinction, though many native speakers don’t follow it consistently:

das gleiche = the same kind / same type of thing
(two different objects or values, but they match)
dasselbe = literally the one and the same identical thing

Examples:

Wir haben das gleiche Auto.
→ We each own a car of the same model, but two separate cars.
Wir fahren mit demselben Auto.
→ We are both in one car together.

For weight:

Mein Gewicht ist heute dasselbe wie gestern.
→ It is exactly the same weight value (70 kg then, 70 kg today).
Mein Gewicht ist heute das gleiche wie gestern.
→ In everyday speech usually means the same thing here; very few people are strict about the distinction.

Also note spelling:

das gleiche = two words
dasselbe = one word (with ss), not das selbe

Why is the verb ist in second position: Mein Gewicht ist heute …?

German main clauses follow the “verb second” (V2) rule:

The conjugated verb must be in second position in the clause.
The first position can be the subject, an adverb, an object, etc.

In your sentence:

Mein Gewicht = first element (subject)
ist = second element (finite verb)
heute das gleiche wie gestern = the rest of the sentence

If you move something else to the front, the verb still stays in second place:

Heute ist mein Gewicht das gleiche wie gestern.
Gestern war mein Gewicht das gleiche wie heute.

All of these keep the verb in the second slot.

Can I change the word order and say Heute ist mein Gewicht das gleiche wie gestern?

Yes, that’s perfectly correct:

Heute ist mein Gewicht das gleiche wie gestern.

Differences:

Mein Gewicht ist heute …
→ starts with the topic “my weight”
Heute ist mein Gewicht …
→ starts with the time “today,” emphasizing “today”

Grammatically both are fine, and the meaning is the same; it’s just a matter of emphasis and style. In speech, Germans like moving time expressions (like heute) to the front fairly often.

Why is Gewicht capitalized?

In German, all nouns are capitalized.
Gewicht is a noun, so it must be written with a capital G:

das Gewicht (the weight)
Mein Gewicht ist heute das gleiche wie gestern.

This is one of the most reliable rules in German spelling: every noun gets a capital letter, regardless of where it appears in the sentence.

Why don’t we say am gestern like “on yesterday”?

In German, words like heute (today), gestern (yesterday), morgen (tomorrow) are adverbs of time, not nouns, so they don’t need a preposition:

heute = today
gestern = yesterday
morgen = tomorrow

You simply say:

Mein Gewicht ist heute das gleiche wie gestern.
literally “My weight is today the same as yesterday.”

Using am (“on the”) only makes sense with days that behave like nouns, e.g.:

am Montag (on Monday)
am 1. Januar (on the 1st of January)

But not:

✗ am gestern
✗ am heute

Those are incorrect.

Could I leave out heute or gestern and still be grammatical?

You can omit one, but it changes what is clear from context:

Without heute:
- Mein Gewicht ist das gleiche wie gestern.
  → “My weight is the same as yesterday.”
  Perfectly grammatical and natural. “Today” is understood from context.
Without gestern:
- Mein Gewicht ist heute das gleiche.
  → “My weight is the same today.”
  Grammatically fine, but it sounds incomplete: the same as what?
  Usually you’d expect a continuation:
- … das gleiche wie gestern.
- … das gleiche wie letzte Woche.

So: grammatically both versions are okay, but you normally specify what it’s the same as, using wie + reference point.

Why is it das gleiche and not das gleichen?

The ending on gleich- follows adjective declension rules. After the definite article das in nominative neuter, the adjective takes the ending -e:

das gleiche (nominative / accusative neuter, with article)

Compare:

der gleiche Mann (masculine nominative)
die gleiche Frau (feminine nominative)
das gleiche Gewicht (neuter nominative)
die gleichen Preise (plural nominative)

Das gleichen would correspond to a different case (e.g. genitive masculine/neuter: des gleichen Mannes), which is not what we need here. After ist, we are in the nominative, not the genitive.

How do you pronounce Gewicht and gleich?

Approximate pronunciations:

Gewicht → /ɡəˈvɪçt/
- Ge- like “guh-”
- -wicht:
  - w like English v
  - i like in sit
  - ch here is the “soft” German ich-sound (as in ich), not like English “k”
  - final t is clearly pronounced
gleich → /ɡlaɪç/
- gl like in English glad
- ei pronounced like English long “i” in my
- final ch again the ich-sound /ç/ (in many accents it’s somewhere between /x/ and /ç/)

Put together:

Mein Gewicht ist heute das gleiche wie gestern.
/maɪn ɡəˈvɪçt ɪst ˈhɔʏtə das ˈɡlaɪçə viː ˈɡɛstɐn/

Is das gleiche capitalized or not? I’ve seen das Gleiche too.

You’ll see both in real life:

das gleiche (adjective phrase)
das Gleiche (nominalized adjective)

Usage:

If you think of gleiche as a normal adjective modifying an understood noun (here: Gewicht), many people write it lowercase:
- Mein Gewicht ist heute das gleiche wie gestern.
If you treat das Gleiche as a standalone noun meaning “the same thing”, it’s capitalized:
- Mein Gewicht ist heute noch genau das Gleiche.
  (= the same as before; “the same thing”)

Dictionaries and style guides generally accept both in a sentence like yours. For learners, it’s safe to prefer das Gleiche when it stands alone as “the same (thing).” Here, either spelling is very unlikely to be marked wrong.