ChatGPT vs DeepSeek for math

Every limit is published. Paid plans also have a monthly fair-use limit on AI cost: Pro $7.50, Max $20, Ultra $42, Studio $85. Using every message on your plan at typical sizes stays under it; very large messages and heavy research use it faster. Every limit, explained.

Math: GPT-6 Sol passed 5 of 5 and DeepSeek V4.1 Flash 5 of 5. DeepSeek V4.1 Flash answered 1.3× sooner at the median, 2.2 s against 1.7 s. DeepSeek V4.1 Flash cost 7.8× less, $0.0090 against $0.0012 for the 5 replies. DeepSeek V4.1 Flash's replies ran 49% longer, in tokens of reply, thinking not counted.

1. 1. A discount, then sales tax

   Everyday. GPT: 3 of 3 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4 Pro the cheapest at $0.0002. The prompt in full.

   GPT-6 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (0.6 s to 1.7 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0013); GPT-6 Sol wrote 45 tokens of reply, DeepSeek V4.1 Flash 41.

   • GPT-6 Sol

     Passed: Final answer 66: right.

     25% off $80 gives $80 × 0.75 = $60.  
     Adding 10% sales tax gives $60 × 1.10 = $66.
     
     Final answer: $66

     400 tokens in, 45 out · 1.7 s · $0.0013 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 66: right.

     $80 × 0.75 = $60 (after 25% discount)
     $60 × 1.10 = $66 (with 10% tax)
     
     Final answer: $66

     440 tokens in, 64 out (23 of them reasoning) · 0.6 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Parasail · September 27, 2026

2. 2. Pens at 3 for $4

   Everyday. GPT: 2 of 3 models passed, GPT-6 Sol the cheapest at $0.0024 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0003. The prompt in full.

   GPT-6 Sol and DeepSeek V4.1 Flash both passed this one. GPT-6 Sol answered sooner (3.3 s to 25.6 s), and DeepSeek V4.1 Flash's reply cost less ($0.0003 to $0.0024); GPT-6 Sol wrote 56 tokens of reply, DeepSeek V4.1 Flash 138.

   • GPT-6 Sol

     Passed: Final answer 13.50: right.

     Three groups of 3 pens cost \(3 \times \$4 = \$12\). One single pen costs \$1.50, bringing the total to \$13.50. Using fewer groups would cost more.
     
     Final answer: $13.50

     402 tokens in, 164 out (108 of them reasoning) · 3.3 s · $0.0024 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer Buy three 3-packs (9 pens) plus one single pen for 13.50.: right.

     **Working:**
     - 3-pack price per pen: $4 ÷ 3 ≈ $1.33 (best value)
     - Buy as many 3-packs as fit: 3 packs = 9 pens = $12, plus 1 single at $1.50 = **$13.50**
     - Check other combinations: 2 packs + 4 singles = $8 + $6 = $14; 1 pack + 7 singles = $14.50; 10 singles = $15
     - The $13.50 option is cheapest.
     
     Final answer: Buy three 3-packs (9 pens) plus one single pen for $13.50.

     442 tokens in, 854 out (716 of them reasoning) · 25.6 s · $0.0003 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Morph · September 27, 2026

3. 3. Compound interest over three years

   Everyday. GPT: 3 of 3 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0002. The prompt in full.

   GPT-6 Sol and DeepSeek V4.1 Flash both passed this one. They took about as long (GPT-6 Sol 1.4 s, DeepSeek V4.1 Flash 1.5 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0014); GPT-6 Sol wrote 62 tokens of reply, DeepSeek V4.1 Flash 104.

   • GPT-6 Sol

     Passed: Final answer 315.25: right.

     After 3 years, the balance is \(2000(1.05)^3=\$2,315.25\). Subtracting the original deposit gives \(2315.25-2000=\$315.25\) in interest.
     
     Final answer: $315.25

     402 tokens in, 62 out · 1.4 s · $0.0014 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 315.25: right.

     **Working:**
     
     - Year 1: $2,000 × 1.05 = $2,100.00
     - Year 2: $2,100.00 × 1.05 = $2,205.00
     - Year 3: $2,205.00 × 1.05 = $2,315.25
     
     Interest earned = $2,315.25 − $2,000.00 = **$315.25**
     
     Final answer: $315.25

     440 tokens in, 186 out (82 of them reasoning) · 1.5 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via CoreWeave · September 27, 2026

4. 4. Four-digit numbers whose digits sum to 9

   Hard. GPT: 3 of 3 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0002. The prompt in full.

   GPT-6 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (1.7 s to 2.5 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0019); GPT-6 Sol wrote 78 tokens of reply, DeepSeek V4.1 Flash 112.

   • GPT-6 Sol

     Passed: Final answer 165: right.

     Subtract 1 from the thousands digit. The four digits then become nonnegative integers that sum to 8. By stars and bars, the number of solutions is \(\binom{8+4-1}{4-1}=\binom{11}{3}=165\). Every solution gives a valid four-digit integer.
     
     Final answer: 165

     378 tokens in, 117 out (39 of them reasoning) · 2.5 s · $0.0019 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 165: right.

     Let the digits be $a,b,c,d$ with $a \ge 1$ (four-digit) and $b,c,d \ge 0$, and $a+b+c+d=9$.
     
     Set $a' = a-1 \ge 0$. Then $a'+b+c+d = 8$.
     
     Number of nonnegative solutions to a sum of 8 across 4 variables:
     
     $$\binom{8+4-1}{4-1} = \binom{11}{3} = 165$$
     
     Final answer: 165

     417 tokens in, 216 out (104 of them reasoning) · 1.7 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Novita · September 27, 2026

5. 5. The highest of three dice is a 5

   Hard. GPT: 3 of 3 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0002. The prompt in full.

   GPT-6 Sol and DeepSeek V4.1 Flash both passed this one. GPT-6 Sol answered sooner (2.2 s to 2.5 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0020); GPT-6 Sol wrote 91 tokens of reply, DeepSeek V4.1 Flash 100.

   • GPT-6 Sol

     Passed: Final answer 61/216: right.

     For the highest number to be exactly 5, all three dice must show 5 or less, but not all can show 4 or less.
     
     \[
     P(\text{highest is }5)=\left(\frac56\right)^3-\left(\frac46\right)^3
     =\frac{125-64}{216}=\frac{61}{216}.
     \]
     
     Final answer: 61/216

     393 tokens in, 122 out (31 of them reasoning) · 2.2 s · $0.0020 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 61/216: right.

     Total outcomes: 6³ = 216.
     
     Max exactly 5 means all dice show ≤ 5, but not all show ≤ 4:
     
     - All ≤ 5: 5³ = 125
     - All ≤ 4: 4³ = 64
     
     So favorable outcomes: 125 − 64 = 61.
     
     Probability = 61/216 (already in lowest terms, since 61 is prime and doesn't divide 216).
     
     Final answer: 61/216

     432 tokens in, 155 out (55 of them reasoning) · 2.5 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via CoreWeave · September 27, 2026

• GPT-6 Astra vs DeepSeek V4 Pro: 5 of 5 each; they took about as long and DeepSeek V4 Pro cost 12.9× less.

• GPT-6 Astra vs DeepSeek V4.1 Flash: 5 of 5 each; DeepSeek V4.1 Flash answered 1.5× sooner at the median and cost 36.8× less.

• GPT-6 Sol vs DeepSeek V4 Pro: 5 of 5 each; GPT-6 Sol answered 1.3× sooner at the median and DeepSeek V4 Pro cost 2.7× less. GPT-6 Sol vs DeepSeek V4 Pro, on every job.

• GPT-6 Sol vs DeepSeek V4.1 Flash: 5 of 5 each; DeepSeek V4.1 Flash answered 1.3× sooner at the median and cost 7.8× less.

• GPT-6 Luna vs DeepSeek V4 Pro: GPT-6 Luna 4 of 5, DeepSeek V4 Pro 5; GPT-6 Luna answered 1.2× sooner at the median and cost 6.7× less. GPT-6 Luna vs DeepSeek V4 Pro, on every job.

• GPT-6 Luna vs DeepSeek V4.1 Flash: GPT-6 Luna 4 of 5, DeepSeek V4.1 Flash 5; DeepSeek V4.1 Flash answered 1.3× sooner at the median and GPT-6 Luna cost 2.4× less. GPT-6 Luna vs DeepSeek V4.1 Flash, on every job.

Every GPT and DeepSeek reply above was checked the same way as every other model's, by the rules published with the prompts: how the math prompts are scored, and each one in full.

• The lineups

  GPT: 3 models, GPT-6 Astra, GPT-6 Sol, and GPT-6 Luna. DeepSeek: 2 models, DeepSeek V4 Pro and DeepSeek V4.1 Flash.

• Price per message

  The least expensive GPT model is GPT-6 Luna (60 messages a day on Pro); the least expensive DeepSeek model is DeepSeek V4.1 Flash (60 messages a day on Pro).

• Context window

  GPT goes up to 1.05M tokens (GPT-6 Astra); DeepSeek up to 1.05M tokens (DeepSeek V4 Pro).

• Images and PDFs

  DeepSeek V4 Pro doesn't read images. DeepSeek V4 Pro and DeepSeek V4.1 Flash get a PDF's text rather than the file itself.

• On the Free plan

  Free's one-time trial of 5 messages covers GPT-6 Sol, GPT-6 Luna, DeepSeek V4 Pro, and DeepSeek V4.1 Flash. Paid plans have every model, with messages every month.

In llmwise, a message to GPT goes to its maker, OpenAI, or through OpenRouter when llmwise can't reach the maker directly. DeepSeek models are served only through OpenRouter, by endpoints that don't store or train on prompts. The Privacy Policy has the details.