Säästän rahaa tekemällä ruokaa kotona sen sijaan, että söisin ulkona.

Rahaa is the partitive singular of raha (money). Finnish uses the partitive for:

• Uncountable / indefinite amounts: You are not saving all your money, just some money.
• “Some of something” ideas: säästää rahaa, juoda vettä, ostaa maitoa, etc.

So:

• Säästän rahaa = I save (some) money / I’m saving money.
• Säästän rahat would sound like you are saving the specific, whole sum of money already known from context.
• Säästän rahan is also possible but would normally mean I will save that (one) sum of money (more definite, one “instance” of money, often a specific cost).

In ordinary “I save money” statements, Finns almost always use the partitive rahaa.

Tekemällä is the third infinitive in the adessive case of the verb tehdä (to do, to make).

• Verb stem: teke- (from tehdä)
• Third infinitive ending: -mA → tekemä
• Adessive case ending: -lla / -llä → tekemällä

This construction (-malla / -mällä) often means “by doing X”, describing the means or manner by which something happens.

So:

• Säästän rahaa tekemällä ruokaa = I save money *by making food*
• Other examples:
  
  • Opin paremmin lukemalla ääneen. = I learn better by reading aloud.
  • Painon voi pudottaa liikkumalla enemmän. = You can lose weight by exercising more.

English often uses a “by -ing” phrase; Finnish uses this third infinitive in adessive (doing + -lla/llä).

Ruokaa is the partitive singular of ruoka (food).

Here it’s used because:

1. We’re talking about an indefinite amount of food (“making food in general,” not one specific dish).
2. Partitive is common with mass nouns when the amount is not specified.

Compare:

• Teen ruokaa. = I’m making (some) food / I cook.
• Teen ruoan. = I’ll make the food (a particular meal, e.g. “I’ll make today’s meal”).

In tekemällä ruokaa kotona, the focus is on doing the activity of cooking food in general, so ruokaa fits naturally.

All three come from koti (home), but with different cases and meanings:

• kotona = “at home” (inside / in that location) – inessive case
• kotiin = “(to) home” (movement toward home) – illative case
• kotoa = “from home” (movement away from home) – elative case

In the sentence:

• tekemällä ruokaa kotona = by cooking food at home

Some contrasts:

• Olen kotona. = I am at home.
• Menen kotiin. = I go home.
• Tulen kotoa. = I come from home.

So kotona is correct because we’re describing where the cooking happens, not movement to or from home.

You can break sen sijaan, että down like this:

• sen = “of that” / “that’s” (genitive of se, that)
• sijaan = “instead (of)” (illative of sija, place/stead)
• että = “that” (a conjunction introducing a clause)

Literally, it’s something like:

• sen sijaan = “in its stead / instead of that”
• sen sijaan, että söisin ulkona ≈ “instead of that, that I would eat out”

In practice, sen sijaan, että + verb is a fixed structure meaning “instead of (doing something)”:

• Luen kirjaa sen sijaan, että katsoisin televisiota.
  = I read a book instead of watching TV.

Söisin is the conditional form of syödä (to eat):

• Present: syön = I eat / I am eating
• Conditional: söisin = I would eat

In the structure sen sijaan, että + verb, it’s very common to use the conditional when you’re comparing what you actually do with a hypothetical alternative:

• Säästän rahaa tekemällä ruokaa kotona sen sijaan, että söisin ulkona.
  = I save money by cooking at home instead of (what I would do otherwise) eating out.

Using söisin highlights that “eating out” is the option I would choose, but I don’t.
You can sometimes see että syön ulkona, but with sen sijaan, että, the conditional söisin is more idiomatic and clearly contrasts the real action with a non-realized alternative.

You could grammatically say:

• Säästän rahaa tekemällä ruokaa kotona sen sijaan, että syön ulkona.

This is understandable, but:

• With syön, the second clause feels more like a simple present fact.
• With söisin, it clearly expresses a would-be alternative (what you would otherwise do).

Native speakers strongly prefer söisin here. It neatly matches the idea:

• “I really cook at home (and save money)
  instead of what I would (otherwise) do, eat out.”

So syön is not strictly “wrong”, but söisin is both more natural and semantically sharper.

Literally, syödä ulkona is “to eat outside / outdoors”.

However, in everyday language it very commonly means:

• “to eat out” (at a restaurant, café, etc.), not at home.

Context often tells you which meaning is intended:

• Onpa ihana ilma, syödään ulkona!
  = What lovely weather, let’s eat outside (literally outdoors).
• Säästän rahaa tekemällä ruokaa kotona sen sijaan, että söisin ulkona.
  = I save money by cooking at home instead of eating out (in restaurants).

Because the contrast is with cooking at home, here syödä ulkona is clearly “eat out.”

Yes, that word order is perfectly fine and natural:

• Tekemällä ruokaa kotona säästän rahaa sen sijaan, että söisin ulkona.

Finnish word order is quite flexible. Moving tekemällä ruokaa kotona to the beginning just shifts the emphasis slightly:

• Original: Säästän rahaa tekemällä ruokaa kotona...
  → Emphasis starts on what you achieve (saving money).
• Changed: Tekemällä ruokaa kotona säästän rahaa...
  → Emphasis starts on how you do it (by cooking at home).

Both are correct; it’s mainly a stylistic/emphasis choice.

Yes, you can say:

• Säästän rahaa, kun teen ruokaa kotona.
  = I save money when I cook at home.

Difference in nuance:

• tekemällä ruokaa kotona = emphasizes means / method:
  
  • I save money *by cooking at home.*
• kun teen ruokaa kotona = emphasizes time / condition:
  
  • I save money *when(ever) I cook at home.*

In many contexts the meaning overlaps a lot, and both are acceptable.
The original sentence then adds the explicit contrast sen sijaan, että söisin ulkona, which goes more naturally with the “by doing X instead of Y” structure using -mällä.

Yes, in this expression the comma is standard:

• sen sijaan, että + clause

Here että introduces a subordinate clause (että söisin ulkona). In Finnish punctuation, such subordinate clauses are normally separated by a comma.

Examples:

• Sen sijaan, että valittaisin, yritän ratkaista ongelman.
• Sen sijaan, että ajaisin autolla, kävelen.

So you should generally write sen sijaan, että with a comma before että when it’s followed by a full clause.