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Biology Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

DNA Reverse Complement Calculator

You can paste DNA or RNA sequence or a FASTA record and get the cleaned sequence, its complement and the reverse complement with 5′ and 3′ labels, then copy or download the result.

Runs in your browserFree · No sign-up · No watermark
DNA/RNA → COMPLEMENTRuns in your browser
Loading the tool…

Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
DNA/RNA → COMPLEMENT
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Biology Tools

About DNA Reverse Complement Calculator

A DNA strand has direction: one end is 5′ and the other 3′, and the two strands run antiparallel. Because bases pair in a fixed way, A with T and C with G, the sequence on one strand tells you the sequence on the other. The reverse complement is that partner strand written in the conventional 5′ to 3′ direction.

This tool cleans pasted sequence first: FASTA headers, line breaks, spaces, digits and punctuation are removed, invalid letters are reported, and you choose DNA or RNA so adenine pairs with thymine or uracil. The cleaned input, the complement read 3′ to 5′ and the reverse complement read 5′ to 3′ are shown separately with copy buttons and a downloadable text report.

What this tool does

The details that matter when you use DNA Reverse Complement Calculator for real work.

  • DNA and RNA pairing

    Switch between DNA (A ↔ T, C ↔ G) and RNA (A ↔ U, C ↔ G); the chosen molecule also controls which letters are valid.

  • Complement and reverse complement

    Both orientations are shown explicitly: the complement read 3′ → 5′ and the reverse complement read 5′ → 3′.

  • FASTA and raw input cleanup

    Paste a header-bearing record or raw sequence; headers, whitespace, digits and punctuation are stripped before the sequence is complemented.

  • Invalid characters reported

    Letters that are not bases are counted and named instead of silently disappearing, and U in DNA mode or T in RNA mode gets a mode-switch hint.

  • Ambiguity codes supported

    IUPAC codes use their standard complements (R with Y, K with M, B with V, D with H), so partially ambiguous sequences still work.

  • Copy and download

    Copy any of the three sequences or download a labelled plain-text report for a lab notebook or report.

How to use DNA Reverse Complement Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Paste the sequence

    Paste raw sequence or a FASTA record into the text box; the sequences appear as soon as the input contains valid bases.

  2. 02

    Choose DNA or RNA

    Pick the molecule that matches the sequence so adenine pairs with thymine or with uracil.

  3. 03

    Read the three sequences

    Check the cleaned input, the complement in 3′ → 5′ orientation and the reverse complement in 5′ → 3′ orientation.

  4. 04

    Fix anything reported

    Warnings list invalid letters and skipped bases; switch the molecule if U or T is being skipped.

  5. 05

    Copy or download

    Use the copy buttons for one sequence or download a text report containing all three.

How this tool works

Works with
DNA/RNA → COMPLEMENT
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Works on nucleotide sequences only; protein or prose input is reported as invalid letters instead of being complemented.
  • Ambiguity codes are complemented by their IUPAC partners, which is a notation convention rather than knowledge of the actual base.
  • Very long sequences are capped in the on-screen boxes, though the copy buttons and the downloaded report include the full sequence.

Privacy and file handling

The sequence you paste stays in this browser tab. Cleaning, complementing and reversing run with JavaScript on your device, so nothing is uploaded, stored or logged, and closing the page discards the input and its result.

Read the full privacy policy

DNA Reverse Complement Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is a reverse complement?
The reverse complement is the sequence of the opposite DNA strand written 5′ to 3′. You get it by replacing every base with its partner (A with T, C with G) and then reversing the order, because the two strands run in opposite directions.
How do I reverse complement a DNA sequence by hand?
Pair each base with its complement first, then read the result backwards. For ATGC the complement is TACG, and reversing it gives GCAT. Doing both steps in one pass from the last base to the first avoids forgetting the reversal.
What is the difference between the complement and the reverse complement?
The complement is aligned with the original but read in the opposite direction, so it is usually written 3′ to 5′. The reverse complement reverses that string, giving the opposite strand in the standard 5′ to 3′ orientation used by primers and databases.
Why does the DNA or RNA mode change the complement of A?
In DNA, adenine pairs with thymine, so A becomes T. In RNA, adenine pairs with uracil, so A becomes U. Choosing the wrong mode shifts that one base type and the warning about skipped U or T bases points it out.
Does the tool accept FASTA files and lowercase letters?
Yes. Paste the record text directly: lines starting with > or ; are skipped, lowercase letters are uppercased, and whitespace, digits and punctuation are removed. The result shows how many header lines were removed so you can confirm the input was read as expected.
What happens to ambiguous bases such as N?
IUPAC ambiguity codes are complemented with their standard partners: R with Y, K with M, B with V, D with H, while S, W, N and X pair with themselves. They stay ambiguous in the result and are not resolved into specific bases.
Can I reverse complement a protein sequence?
No. The tool works on nucleotide sequences only, so protein letters such as E, F or P are reported as invalid characters and removed. If a protein sequence is pasted by mistake the warning lists the letters that were skipped.
Are the sequences uploaded or stored anywhere?
No. Cleaning, complementing and reversing all run with JavaScript in this browser tab, so the sequence is never uploaded, stored or logged, and closing the page discards it.

Background reading

Format guides that explain the trade-offs behind DNA Reverse Complement Calculator.