The Complete Guide to ATS Resume Optimization in 2025

What Is an Applicant Tracking System (ATS)?

An Applicant Tracking System (ATS) is software used by employers to collect, filter, organise, and rank job applications before a human recruiter sees them. If you've applied to a job at a company with more than 50 employees in the past decade, there's a very high probability your resume was processed by an ATS first.

ATS software was originally developed to help HR departments manage the administrative burden of recruitment — tracking where each candidate was in the hiring process, storing resumes, and scheduling interviews. But as online job applications made it possible to apply to hundreds of jobs with a single click, the volume of applications per role skyrocketed. ATS systems evolved to include automated screening and ranking features to help recruiters deal with hundreds or thousands of applications per open role.

Today, estimates suggest that 70–99% of large employers use ATS software, and studies by Harvard Business Review suggest that ATS filters eliminate 75% of resumes before a human recruiter ever sees them. Understanding how these systems work isn't optional — it's essential to your job search strategy.

How ATS Systems Actually Screen Resumes

Most ATS systems screen resumes through a combination of keyword matching, formatting parsing, and scoring algorithms. Here's what actually happens when you submit your application:

Step 1: Resume Parsing

The ATS first "parses" your resume — extracting text and attempting to classify it into structured fields: name, contact information, work experience, education, skills, certifications. This is where formatting problems cause the most damage. If your resume uses tables, columns, text boxes, or headers/footers that the parser can't read, your information ends up in the wrong fields or lost entirely.

Step 2: Keyword Matching

The system then compares the extracted text to the job description, looking for keyword matches. Skills listed in the job description that appear in your resume increase your score. Skills that are missing reduce it. The system looks for both exact matches ("Python") and sometimes semantic matches ("machine learning" might also match "ML").

Step 3: Scoring and Ranking

Candidates are scored and ranked. Recruiters typically only review the top 10–20% of ranked applicants, which means that even highly qualified candidates can be filtered out if their resume doesn't score well against the automated criteria.

Step 4: Keyword Density Analysis

Some ATS systems also analyse keyword density — how many times relevant terms appear. This is why simply listing skills in a dedicated section isn't enough; ideally, key skills appear both in your skills section and naturally in your work experience descriptions.

The 7 Most Common ATS Resume Mistakes

1. Using Multi-Column Layouts

Multi-column resumes look professional to a human eye but are a disaster for ATS parsers. When a parser encounters two columns, it often reads across both columns simultaneously — "Project Manager | Collaborated with" — instead of reading each column separately. Your carefully crafted experience descriptions turn into garbled nonsense in the system's database.

Fix: Use a single-column layout for ATS submissions. You can keep a visually appealing design for PDF submissions to humans, but create a plain single-column version for online applications.

2. Storing Information in Headers and Footers

Putting your name, phone number, or email in the document's header or footer seems like a natural design choice, but many ATS parsers completely ignore header and footer content — it's treated as document metadata rather than resume content. Recruiters may genuinely be unable to contact you because your contact information was stored where the system couldn't read it.

Fix: Keep all your information in the main body of the document, not in Word's header/footer feature.

3. Using Images, Graphics, and Icons

Infographic resumes with skill bars, icons, and photos look impressive in portfolios but are completely unreadable to ATS. Text inside images cannot be extracted by parsers. A resume that shows your skills as a visual bar chart gives the ATS no information about those skills at all.

Fix: Describe skills as plain text. "Advanced proficiency in Python and Django" communicates the same information as a skill bar and is actually readable by ATS.

4. Non-Standard Section Headings

ATS systems are trained to recognise standard section labels: "Work Experience," "Education," "Skills," "Certifications." Creative alternatives like "My Journey," "What I've Built," or "Things I Know" confuse parsers and may cause your content to be miscategorised or ignored.

Fix: Use standard, conventional section headings. Creativity in naming doesn't improve your chances — it harms them at the ATS stage.

5. Missing Keywords from the Job Description

This is the biggest and most common mistake. Candidates describe their experience in their own words, which may be accurate but don't match the specific terminology in the job description. An employer looking for a "Digital Marketing Manager" who needs someone with "SEM experience" will filter out a resume that says "paid search advertising" — even though they mean the same thing.

Fix: Read every job description carefully and mirror its exact language. If they say "SEM," use "SEM." If they say "cross-functional collaboration," use that phrase. Don't substitute synonyms.

6. Saving in the Wrong File Format

PDF is generally safe for ATS, as modern systems can extract text from PDFs. However, scanned PDFs (images of documents) are completely unreadable. DOCX is the safest format as it contains fully structured text. Avoid sending image files, Google Docs links, or unusual formats.

7. Inconsistent Date Formatting

ATS systems try to parse employment dates to calculate your experience duration. Inconsistent formatting ("Jan 2022" in one place and "01/2022" in another, or "Present" vs. "Current") can cause parsing errors that make your experience appear shorter than it is.

Fix: Use consistent, unambiguous date formats throughout. "Month YYYY" (e.g., "March 2022") is widely recognised.

How to Identify Keywords in Job Descriptions

Effective keyword extraction from job descriptions is a skill that significantly improves your ATS scores. Here's a systematic approach:

Identify required skills — Look for phrases like "must have," "required," "you will need," or bullet points listed under "Requirements." These are mandatory keywords.
Identify preferred skills — Phrases like "nice to have," "preferred," or "bonus" indicate secondary keywords that improve your score but aren't eliminators.
Note job title variations — If a job is titled "Senior Software Engineer" but also mentions "Tech Lead" in the description, include both terms in your resume if they apply.
Find industry-specific terminology — Every industry has jargon. Match the specific terminology used in the posting rather than generic alternatives.
Include certifications and tools by name — "AWS Certified Solutions Architect," "Salesforce," "HubSpot," "Figma" — named tools and certifications score much better than general descriptions.

Checking Your Resume with DocsConverter's ATS Checker

Our free ATS Resume Checker analyses your resume against job descriptions to identify missing keywords and potential formatting issues. Here's how to use it effectively:

Paste your resume text — Copy the full text of your resume into the resume field. Make sure to include all sections: summary, experience, education, and skills.
Paste the job description — Copy the complete job posting, including the job title, requirements, responsibilities, and any preferred qualifications.
Review your ATS score — The tool calculates a keyword match percentage. Scores above 70% indicate a strong keyword match. Scores below 50% suggest significant optimisation is needed.
Identify missing keywords — The checker highlights important keywords from the job description that don't appear in your resume. These are your optimisation targets.
Review formatting warnings — The tool flags potential parsing issues like tables, columns, or non-standard headings.
Optimise and re-check — Update your resume to incorporate missing keywords naturally, then paste the updated version to see your improved score.

Building an ATS-Optimised Resume with DocsConverter

Our Resume Builder offers six templates, all designed to be ATS-parseable while looking professional. When building your resume:

Choose Classic or Minimalist templates for maximum ATS compatibility — single column, standard fonts, clear section headings.
Use the Skills section to list specific tools, technologies, and competencies using the exact terminology from job descriptions.
Write experience bullet points that begin with strong action verbs and quantify achievements: "Increased conversion rate by 23% through A/B testing" scores better than "Worked on website improvements."
Include a professional summary at the top that contains key role-specific keywords — this section is heavily weighted by many ATS systems.
Download as PDF — Our Resume Builder generates a properly structured PDF with selectable, parseable text (not an image-based PDF).

The Difference Between ATS Optimisation and "Keyword Stuffing"

A concern candidates often raise: "Won't putting all these keywords in my resume make it look like spam?" This is a valid concern, but the distinction is natural integration vs. keyword stuffing.

Keyword stuffing looks like this: "Python Python Python JavaScript React developer with Python skills who uses Python." It's obvious, reads poorly, and will be flagged by more sophisticated ATS systems and rejected by human reviewers.

Natural integration looks like this: "Led development of a Python-based data pipeline using React for the front-end dashboard, reducing reporting time by 40%." The same keywords appear once, in context, with a quantified achievement — readable by both ATS and humans.

The goal is to mirror the job description's language within naturally readable experience descriptions, not to repeat keywords mechanically.

After the ATS: Optimising for Human Reviewers

Passing the ATS is necessary but not sufficient. Once a human recruiter looks at your resume, different criteria apply:

Quantified achievements — Numbers make accomplishments concrete and credible. "Managed a team" vs. "Managed a team of 12 engineers across 3 time zones."
Logical chronology — Employment gaps, short tenures, and unexplained job changes raise questions. Be prepared to address these in interviews.
Consistent narrative — Your career history should tell a coherent story of progression. Random-seeming career changes need context.
Clean formatting — Even in ATS-optimised templates, consistency in fonts, spacing, and alignment matters to human reviewers.

Frequently Asked Questions About ATS Optimisation

What ATS score should I aim for?
A keyword match score above 70% on our ATS Checker indicates a strong match. However, scores are guides — a 65% score with highly relevant experience will often outperform a 85% score with a superficial match.

Should I have different resume versions for different jobs?
Yes — this is one of the highest-impact things you can do in your job search. A tailored resume that mirrors each job description's specific language consistently outperforms a generic resume, both at the ATS stage and with human reviewers.

Does the ATS see my entire resume?
Only the parseable text. Anything stored in images, graphics, headers/footers, or text boxes may not be extracted. Our ATS Resume Checker flags these issues.

Is a one-page resume better for ATS?
ATS systems don't penalise multi-page resumes. The one-page rule is a human preference, particularly for entry-level candidates. For experienced professionals, two pages is appropriate and often expected.

Can ATS read PDF resumes?
Modern ATS can read text-based PDFs (where you can select and highlight the text). Scanned PDFs — photos of paper documents — are unreadable. Always use a digitally created PDF, like those generated by DocsConverter's Resume Builder.