What does saving $52.50 a month on tom yum mean?
It means making at home costs $38.75 for 5 days while buying costs $91.25 for the same 5 days — a gap of $10.50 a serving, $52.50 a month, $630.00 over a year. The home total is 42.47% of the buying total, so every bought serving of tom yum you replace with a homemade serving keeps $10.50 in your pocket. The break-even buying price is $7.75 a day: a restaurant bowl of tom yum at any price above $7.75 loses to homemade, and only a bowl of tom yum at or below $7.75 ties or beats it.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Home total per month | days × home cost per serving | $38.75 — 5 × $7.75. |
| Buying total per month | days × buying cost per serving | $91.25 — 5 × $18.25. |
| Monthly saving | buying total − home total | $52.50 — $91.25 − $38.75. |
| Yearly saving | monthly saving × 12 | $630.00 — $52.50 × 12. |
| Break-even buying price | home cost per serving | $7.75 a day — the bought price at which home stops winning. |
| Home cost behind a target saving | buying cost − target saving ÷ days | $7.75 — $18.25 − $52.50 ÷ 5. |
| Buying cost behind a target saving | home cost + target saving ÷ days | $18.25 — $7.75 + $52.50 ÷ 5. |
| Days behind a target saving | target saving ÷ (buying cost − home cost) | 5 — $52.50 ÷ $10.50. |
Three things to check before you trust the number
First, the home cost must be the full per-serving cost: shrimp, mushrooms, lemongrass and lime, priced per serving, plus the lime and chilies you always finish it with. Mushrooms are cheap all year, but the shrimp and the broth are where the money sits in a rich version — pricing only the mushrooms makes homemade look cheaper than it is. Second, the buying price must be what you actually pay per serving, including delivery or service charges on that tom yum — a menu price without the extras understates the buying total. Third, the day count must match reality: 5 days means a serving of tom yum on 5 days of the month, whether homemade or bought, and counting days you skip inflates both totals and the saving.
Worked example
Days 5, home $7.75, buying $18.25. Home total: 5 × $7.75 = $38.75. Buying total: 5 × $18.25 = $91.25. Monthly saving: $91.25 − $38.75 = $52.50. Yearly saving: $52.50 × 12 = $630.00. Drop to 2 days and the saving falls to $21.00 a month; at 5 days it is $52.50 a month; rise to 10 days and it is $105.00 a month; rise to 15 days and it climbs to $157.50 a month; rise to 30 days and it reaches $315.00 a month. The saving scales exactly with the days, because the $10.50 per-serving gap never changes.
Every branch, checked
A home cost of $8.25 with the same days and buying cost gives home $41.25 vs buying $91.25, a saving of $50.00 a month. A buying cost of $17.75 with the same days and home cost gives home $38.75 vs buying $88.75, a saving of $50.00 a month. Twelve days with the same home and buying costs gives home $77.50 vs buying $182.50, a saving of $105.00 a month. Thirty days with the same home and buying costs gives home $232.50 vs buying $547.50, a saving of $315.00 a month. Each branch changes exactly one input, so the difference from $52.50 isolates that input.
The reverses, worked backwards
The home cost behind $52.50 a month saved is $7.75: at $7.75 the figures are home $38.75 vs buying $91.25, a saving of $52.50 a month; at $7.25 they are home $36.25 vs buying $91.25, a saving of $55.00 a month, and at $8.25 they are home $41.25 vs buying $91.25, a saving of $50.00 a month — a $0.50 step moves the saving by $2.50, because it applies to all 5 days. The buying cost behind $52.50 a month saved is $18.25: at $17.75 the saving is $50.00 a month, and at $18.75 it is $55.00 a month — a $0.50 step moves the saving by $2.50, because it applies to all 5 days. The days behind $52.50 a month saved are 5: at 0 days the saving is $0.00 a month, and at 10 days it is $105.00 a month — five days down moves the saving by $52.50, and five days up moves it by $52.50.
What the defaults assume
The defaults assume one serving of tom yum on each of 5 days, a steady $7.75 home cost and a steady $18.25 bought price, all year. Real tom yum habits cluster around weekday lunches in cold weather, so the honest use is to enter your average month, or to run the calculator once per stretch of the year and add the stretches. A pot of tom yum also rewards batch cooking: a big pot of tom yum makes many servings, and a pot that makes 5 servings divides its shrimp, mushroom, lemongrass and lime cost by 5. Zero days is the honest edge: home $0.00 vs buying $0.00, exactly even. Negative inputs are rejected, and a home cost above the buying price flips the verdict honestly: at a buying price of $6.75 against $7.75 home, home costs $5.00 more a month over 5 days, and buying wins.
Who uses this
A daily tom yum buyer weighing a homemade habit: the $52.50 monthly gap is the prize, and the $630.00 yearly gap is the reason to keep shrimp, mushrooms and lemongrass on hand. A parent planning family lunches: the home line prices a serving of tom yum made at home against the serving of tom yum bought at the restaurant on the way to work. A home cook testing prices: the break-even of $7.75 a day is the floor a home cook must beat, and the buying line is the price a customer compares against. A household cutting food spending without giving up tom yum: the days line shows exactly how much each skipped tom yum day is worth.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is in the inputs. A home cost that omits the shrimp or the broth, a buying price that omits delivery, or a day count that includes skipped days will each move the answer by exactly the amount of the error, every month. The model does not include your time, the cost of a soup pot bought once, or the value of a restaurant bowl of tom yum you enjoy more — price those separately, and re-check the comparison when ingredient or restaurant prices change. This page is a calculation tool, not financial advice.
Cite this calculator
Spicy tom yum soup $7.75 vs $18.25, over 5 days: home $38.75 vs $91.25, saves $52.50 a month, $630.00 a year. Break-even price $7.75 a day. Free calculator. Source: Bright Side Kit, https://brightoolbox.com/making-tom yum-at-home-vs-buying-tom yum/, accessed 1 November 2026 (2026-11-01).
Frequently asked questions
What counts in the home cost per serving?
Everything in one serving: shrimp, mushrooms, lemongrass and lime, priced per serving of tom yum, plus the lime and chilies you finish it with. A pot of tom yum that makes 5 servings divides its shrimp, mushroom, lemongrass and lime cost by 5; leaving out the shrimp understates the home line.
Should I use shrimp, or chicken?
Whichever you actually cook with — the method is the same, the cost is what moves. Shrimp makes a richer bowl and a higher home line; chicken is cheaper and still makes a satisfying bowl. Enter the price of the version you make, not the version in a recipe book.
Should I count my time spent preparing it?
Not in this comparison, which prices ingredients against the restaurant price. If your time matters to you, value it separately: at $20.00 an hour, an hour of preparation a month adds $20.00 to the home line.
Why is the break-even exactly the home cost?
Because home wins whenever the bought price exceeds the home cost per serving: at a bought price of $7.75 the two totals tie, and above it every serving saves the difference. That is why the break-even buying price is $7.75 a day.
Does buying ever win?
Yes — whenever the home cost rises above the bought price. At a buying price of $6.75 against $7.75 home, home costs $5.00 more a month over 5 days, and buying wins by exactly that amount.
How do I use the yearly saving?
Multiply the monthly saving by 12: $52.50 × 12 = $630.00. That is the year total if the habit holds steady; for a habit that runs only part of the year, multiply by the months it actually runs.