ChatGPT vs DeepSeek for math

Every limit is published. Paid plans also have a monthly fair-use limit on AI cost: Plus $3.75, 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-6.1 Sol passed 5 of 5 and DeepSeek V4.1 Flash 5 of 5. DeepSeek V4.1 Flash answered 1.9× sooner at the median, 1.8 s against 0.9 s. DeepSeek V4.1 Flash cost 3.4× less, $0.0043 against $0.0012 for the 5 replies. DeepSeek V4.1 Flash's replies ran 15% longer, in tokens of reply, thinking not counted.

1. 1. A discount, then sales tax

   Everyday. GPT: 4 of 4 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0001. The prompt in full.

   GPT-6.1 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (0.7 s to 1.5 s), and DeepSeek V4.1 Flash's reply cost less ($0.0001 to $0.0006); GPT-6.1 Sol wrote 39 tokens of reply, DeepSeek V4.1 Flash 41.

   • GPT-6.1 Sol

     Passed: Final answer 66: right.

     Discounted price: $80 × 0.75 = $60  
     After sales tax: $60 × 1.10 = $66
     
     Final answer: $66

     402 tokens in, 39 out · 1.5 s · $0.0006 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 66: right.

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

     440 tokens in, 63 out (22 of them reasoning) · 0.7 s · $0.0001 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 7, 2026

2. 2. Pens at 3 for $4

   Everyday. GPT: 3 of 4 models passed, GPT-6.1 Sol the cheapest at $0.0010 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0004. The prompt in full.

   GPT-6.1 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (0.9 s to 2.4 s), and DeepSeek V4.1 Flash's reply cost less ($0.0004 to $0.0010); GPT-6.1 Sol wrote 89 tokens of reply, DeepSeek V4.1 Flash 146.

   • GPT-6.1 Sol

     Passed: Final answer Buy three 3-pen bundles and one single pen for 13.50.: right.

     Three singles cost $4.50, so each 3-for-$4 bundle saves $0.50. Use as many bundles as possible: 3 bundles give 9 pens, then buy 1 single.
     
     Cost: \(3 \times \$4 + \$1.50 = \$13.50\).
     
     Final answer: Buy three 3-pen bundles and one single pen for $13.50.

     404 tokens in, 127 out (38 of them reasoning) · 2.4 s · $0.0010 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer Buy 3 packs of 3 (9 pens) plus 1 single pen, for 13.50.: right.

     3-pack rate: $4/3 ≈ $1.33 per pen, cheaper than $1.50 singles.
     
     Options:
     - 3 packs (9 pens) + 1 single = $12 + $1.50 = $13.50
     - 2 packs (6) + 4 singles = $8 + $6 = $14.00
     - 1 pack + 7 singles = $4 + $10.50 = $14.50
     - 10 singles = $15.00
     
     Best is 3 packs plus 1 single pen.
     
     Final answer: Buy 3 packs of 3 (9 pens) plus 1 single pen, for $13.50.

     442 tokens in, 291 out (145 of them reasoning) · 0.9 s · $0.0004 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 7, 2026

3. 3. Compound interest over three years

   Everyday. GPT: 4 of 4 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-6.1 Sol and DeepSeek V4.1 Flash both passed this one. GPT-6.1 Sol answered sooner (1.7 s to 2.1 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0007); GPT-6.1 Sol wrote 64 tokens of reply, DeepSeek V4.1 Flash 72.

   • GPT-6.1 Sol

     Passed: Final answer 315.25: right.

     After 3 years, the balance is:
     \[
     2000(1.05)^3 = \$2,315.25
     \]
     
     Interest earned:
     \[
     \$2,315.25 - \$2,000 = \$315.25
     \]
     
     Final answer: $315.25

     404 tokens in, 64 out · 1.7 s · $0.0007 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 315.25: right.

     A = P(1 + r)^n = 2000(1.05)^3
     
     1.05³ = 1.157625
     2000 × 1.157625 = 2315.25
     Interest = 2315.25 − 2000 = 315.25
     
     Final answer: $315.25

     441 tokens in, 111 out (39 of them reasoning) · 2.1 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 8, 2026

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

   Hard. GPT: 4 of 4 models passed, GPT-6 Luna the cheapest at $0.0001 · DeepSeek: 2 of 2 models passed, DeepSeek V4.1 Flash the cheapest at $0.0003. The prompt in full.

   GPT-6.1 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (0.7 s to 2.7 s), and DeepSeek V4.1 Flash's reply cost less ($0.0003 to $0.0011); GPT-6.1 Sol wrote 108 tokens of reply, DeepSeek V4.1 Flash 105.

   • GPT-6.1 Sol

     Passed: Final answer 165: right.

     Let the digits be \(a,b,c,d\), with \(a\ge1\). Set \(x=a-1\). Then
     \[
     x+b+c+d=8,
     \]
     where all four variables are nonnegative. Each resulting digit is automatically at most 9.
     
     By stars and bars, the number of solutions is
     \[
     \binom{8+4-1}{4-1}=\binom{11}{3}=165.
     \]
     
     Final answer: 165

     380 tokens in, 147 out (39 of them reasoning) · 2.7 s · $0.0011 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 165: right.

     Let the digits be a, b, c, d with a ≥ 1 (it's a four-digit number) and b, c, d ≥ 0, and a+b+c+d = 9.
     
     Substitute a = a' + 1 where a' ≥ 0:
     a' + b + c + d = 8
     
     Number of non-negative solutions = C(8+3, 3) = C(11, 3) = 165.
     
     Final answer: 165

     417 tokens in, 197 out (92 of them reasoning) · 0.7 s · $0.0003 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 8, 2026

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

   Hard. GPT: 4 of 4 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-6.1 Sol and DeepSeek V4.1 Flash both passed this one. DeepSeek V4.1 Flash answered sooner (1.0 s to 1.8 s), and DeepSeek V4.1 Flash's reply cost less ($0.0002 to $0.0008); GPT-6.1 Sol wrote 87 tokens of reply, DeepSeek V4.1 Flash 81.

   • GPT-6.1 Sol

     Passed: Final answer (61/216 ): right.

     The highest number is exactly 5 if all three dice show at most 5, but not all show at most 4.
     
     \[
     P(\max=5)=\left(\frac56\right)^3-\left(\frac46\right)^3
     =\frac{125-64}{216}=\frac{61}{216}.
     \]
     
     Final answer: \(\frac{61}{216}\)

     395 tokens in, 87 out · 1.8 s · $0.0008 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

   • DeepSeek V4.1 Flash

     Passed: Final answer 61/216: right.

     Count outcomes where all three dice are ≤ 5, then subtract those where all are ≤ 4 (so no 5 appears):
     
     - All ≤ 5: 5³ = 125
     - All ≤ 4: 4³ = 64
     
     Favorable outcomes: 125 − 64 = 61, out of 216 total.
     
     Final answer: 61/216

     433 tokens in, 150 out (69 of them reasoning) · 1.0 s · $0.0002 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 8, 2026

• GPT-6 Astra vs DeepSeek V4 Pro: 5 of 5 each; they took about as long and DeepSeek V4 Pro cost 9.7× less.

• GPT-6 Astra vs DeepSeek V4.1 Flash: 5 of 5 each; DeepSeek V4.1 Flash answered 2.8× sooner at the median and cost 34.2× less.

• GPT-6.1 Sol vs DeepSeek V4 Pro: 5 of 5 each; GPT-6.1 Sol answered 1.5× sooner at the median and cost about the same.

• GPT-6.1 Sol vs DeepSeek V4.1 Flash: 5 of 5 each; DeepSeek V4.1 Flash answered 1.9× sooner at the median and cost 3.4× less.

• GPT-6 Sol vs DeepSeek V4 Pro: 5 of 5 each; GPT-6 Sol answered 1.2× sooner at the median and DeepSeek V4 Pro cost 2.1× 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 2.3× sooner at the median and cost 7.2× 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 8.9× 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 2.4× sooner at the median and GPT-6 Luna cost 2.5× 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: 4 models, GPT-6 Astra, GPT-6.1 Sol, 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

  None of these models is on the Free plan. Paid plans have them, with messages every month: GPT-6 Astra from Pro up.

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.