DNA & RNA Reverse Complement Tool

Generate a reverse complement, complement, or reverse sequence using standard IUPAC nucleotide codes.

How to use this tool

Enter one or more DNA or RNA sequences as plain text or FASTA, then choose the operation you need. Each FASTA record is processed independently.

Reverse complement: Reverses the sequence and replaces every nucleotide with its complementary code.
Reverse: Reads the sequence from last character to first without changing its codes.
Complement: Replaces each nucleotide with its complement while preserving sequence order.
IUPAC codes: Supports R↔Y, K↔M, B↔V, D↔H, S, W, N, and the gap characters - and .
Molecule type: Auto detects T as DNA and U as RNA. Select DNA or RNA when a sequence contains neither.
Browser limits: Accepts up to 1,000,000 sequence characters, 1,000 FASTA records, and 1,000 characters per header.
FASTA files: Load a local FASTA file to inspect, edit, validate, and transform its records without uploading it.

DNA uses A↔T; RNA uses A↔U. Do not mix T and U within one record. Preserve the original letter case or convert output to uppercase or lowercase.

Enter Nucleic Acid Sequence

DNA or RNA Sequence

Load FASTA FileNo file selected

Molecule type

Length: 0Valid: —

Try an example:

Sequences and loaded files are processed entirely in your browser. Nothing is uploaded or stored.

This tool accepts up to 1,000,000 sequence characters and 1,000 FASTA records. These limits help prevent browser slowdowns, especially on mobile devices. Split larger datasets into smaller batches.

Select Transformation

Result

DNA: A↔T | RNA: A↔U | IUPAC ambiguity codes supported

How it works

What is a nucleic acid reverse complement?

A reverse complement is formed by two operations: first the sequence is reversed, then each base is replaced with its Watson-Crick complement. DNA uses thymine (A↔T), RNA uses uracil (A↔U), and cytosine pairs with guanine (C↔G) in both.

The result represents the complementary strand written in the conventional 5′ → 3′ direction.

IUPAC ambiguity codes are complemented as groups: R↔Y, K↔M, B↔V, and D↔H. The self-complementary codes S, W, and N remain unchanged, as do the gap characters - and .

IUPAC nucleotide codes and their complements
Code	Represents	Complement
A	Adenine	T (DNA) or U (RNA)
C	Cytosine	G
G	Guanine	C
T / U	Thymine / Uracil	A
R	A or G	Y
Y	C or T/U	R
S	G or C	S
W	A or T/U	W
K	G or T/U	M
M	A or C	K
B	C, G, or T/U	V
D	A, G, or T/U	H
H	A, C, or T/U	D
V	A, C, or G	B
N	Any base	N
. / -	Gap	Unchanged

Original 5′ → 3′G A T T A C AReversed 3′ → 5′A C A T T A GReverse complement 5′ → 3′T G T A A T C

Sequence easter egg: Gattaca

What is a complement without reversing?

A complement replaces every base with its Watson-Crick partner without changing the input order. For a 5′ → 3′ input sequence, the aligned complement is the opposite strand written 3′ → 5′.

Original 5′ → 3′G A T T A C AComplement 3′ → 5′C T A A T G T

What is a reverse without complementing?

A reverse reads the original sequence backwards, from the last base to the first, without changing any bases. This is less often biologically meaningful by itself, but it can help when checking sequence orientation or palindromes.

Original 5′ → 3′G A T T A C AReversed 3′ → 5′A C A T T A G