What is the reverse complement?
Paste or type a DNA or RNA sequence, written 5′ to 3′. The reverse complement calculator gives the partner strand read 5′ to 3′, with the complement and the reverse, and handles the IUPAC codes for mixed bases such as R, Y and N.
- Reverse complement (5′ to 3′)
- GCTAACGTACGCAT
The reverse complement (5′ to 3′) is GCTAACGTACGCAT.
- Complement (3′ to 5′)
- TACGCATGCAATCG
- Reverse (3′ to 5′)
- CGATTGCATGCGTA
- Length
- 14
- Read as
- DNA
Reverse complement (5′ to 3′): GCTAACGTACGCAT. The reverse complement (5′ to 3′) is GCTAACGTACGCAT.
How to calculate
Gives the reverse complement of a DNA or RNA sequence, read 5′ to 3′, with the complement and the reverse, for the bases A, C, G, T or U and the IUPAC codes for mixed bases.
Example with the default inputs (Sequence (5′ to 3′) ATGCGTACGTTAGC): The reverse complement (5′ to 3′) is GCTAACGTACGCAT.
Method: Complement each base (A–T, or A–U in RNA; G–C; R–Y; K–M; B–V; D–H; S, W and N pair with themselves), then reverse the order.
- The sequence is written 5′ to 3′, as is usual; the reverse complement is the partner strand, also written 5′ to 3′.
- A sequence with a U is read as RNA, and its complement uses U; a sequence may not have both T and U.
- Upper and lower case are kept as typed.
Worked examples
Each example is checked against the calculator on every build.
- Sequence (5′ to 3′) ATGCGTACGTTAGC gives Reverse complement (5′ to 3′) GCTAACGTACGCAT, Complement (3′ to 5′) TACGCATGCAATCG, Reverse (3′ to 5′) CGATTGCATGCGTA, Length 14, Read as DNA.Source: OpenStax, Biology 2e, §14.2 DNA Structure and Sequencing (A pairs with T and G with C; the two strands are antiparallel), https://openstax.org/books/biology-2e/pages/14-2-dna-structure-and-sequencing (retrieved 2026-10-18)
- Sequence (5′ to 3′) AUGGCUAAC gives Reverse complement (5′ to 3′) GUUAGCCAU, Complement (3′ to 5′) UACCGAUUG, Read as RNA.Source: NC-IUB, Nomenclature for Incompletely Specified Bases in Nucleic Acid Sequences, Recommendations 1984 (Table 1: R = A or G, Y = C or T, K = G or T, M = A or C, S = G or C, W = A or T, B, D, H, V, N; Table 2 complements; sequences run 5′ to 3′; T and U are synonyms), https://iubmb.qmul.ac.uk/misc/naseq.html (retrieved 2026-10-18); OpenStax, Biology 2e, §14.2 DNA Structure and Sequencing (A pairs with T and G with C; the two strands are antiparallel), https://openstax.org/books/biology-2e/pages/14-2-dna-structure-and-sequencing (retrieved 2026-10-18)
- Sequence (5′ to 3′) ACGTRYKMSWBDHVN gives Reverse complement (5′ to 3′) NBDHVWSKMRYACGT, Complement (3′ to 5′) TGCAYRMKSWVHDBN.Source: NC-IUB, Nomenclature for Incompletely Specified Bases in Nucleic Acid Sequences, Recommendations 1984 (Table 1: R = A or G, Y = C or T, K = G or T, M = A or C, S = G or C, W = A or T, B, D, H, V, N; Table 2 complements; sequences run 5′ to 3′; T and U are synonyms), https://iubmb.qmul.ac.uk/misc/naseq.html (retrieved 2026-10-18)
- Sequence (5′ to 3′) >EcoRI site 1 gaattc 6 gives Reverse complement (5′ to 3′) gaattc, Length 6.Source: OpenStax, Biology 2e, §14.2 DNA Structure and Sequencing (A pairs with T and G with C; the two strands are antiparallel), https://openstax.org/books/biology-2e/pages/14-2-dna-structure-and-sequencing (retrieved 2026-10-18)
How it works
The sequence is read 5′ to 3′. Each symbol is replaced by its partner, then the order is reversed:
| Symbol | Means | Partner |
|---|---|---|
| A | adenine | T (U in RNA) |
| T or U | thymine, uracil | A |
| G | guanine | C |
| C | cytosine | G |
| R | A or G | Y |
| Y | C or T | R |
| K | G or T | M |
| M | A or C | K |
| B | C, G or T | V |
| V | A, C or G | B |
| D | A, G or T | H |
| H | A, C or T | D |
| S, W, N | G or C; A or T; any | itself |
The partners of R and Y follow from Table 1 of the IUPAC recommendations and the base pairs: R (A or G) pairs with T or C, which is Y. In RNA, read T as U throughout the table (Y is C or U, K is G or U, W is A or U, and so on): the codes and their partners are the same, and only A’s partner is written U.
Outputs. The reverse complement is the partner strand read 5′ to 3′. The complement is the partner of each symbol in the order typed (it reads 3′ to 5′). The reverse is the sequence typed, backwards, with no symbol changed. Length counts the symbols, and read as says DNA or RNA.
Rules. Before anything else, lines that start with > (FASTA headers) are dropped, and spaces, tabs, line breaks and digits are removed. The rest must be the letters A, C, G, T, U, R, Y, K, M, B, V, D, H, S, W or N, in upper or lower case; anything else gives no answer, and so does an empty sequence. A sequence with a U is RNA: A pairs with U. A sequence with no U is DNA: A pairs with T. A sequence with both T and U gives no answer. Each output symbol keeps the case of the symbol it comes from. The box takes up to 10,000 characters.
Worked examples by hand
ATGCGTACGTTAGC (the default). Complement, symbol by symbol: TACGCATGCAATCG. Reversed: GCTAACGTACGCAT. The reverse of the sequence typed is CGATTGCATGCGTA. Length 14.
RNA, AUGGCUAAC. The U makes it RNA, so A pairs with U. Complement UACCGAUUG; reverse complement GUUAGCCAU.
Every IUPAC symbol, ACGTRYKMSWBDHVN. Complement TGCAYRMKSWVHDBN; reverse complement NBDHVWSKMRYACGT.
A FASTA entry with numbers. “>EcoRI site” on the first line, then “1 gaattc 6”. The header, the spaces and the digits are dropped, leaving gaattc. Its complement is cttaag, which reversed is gaattc: the EcoRI site is its own reverse complement.
Other questions people ask
What is a reverse complement?
It is the sequence of the partner strand, written 5′ to 3′ like any sequence. The two strands of DNA are antiparallel, so the partner strand runs the other way: replace each base with its pair (A with T, G with C), then read the result backwards.
How do I find the reverse complement of a DNA sequence?
Write the complement of each base (A to T, T to A, G to C, C to G), then reverse the order. For 5′-ATGC-3′, the complement is TACG and the reverse complement is 5′-GCAT-3′.
What is the difference between the complement and the reverse complement?
The complement pairs each base but keeps the order, so it reads 3′ to 5′ under the sequence typed. The reverse complement also reverses the order, so it reads 5′ to 3′. Primers and probes are written as reverse complements.
How does it handle RNA?
If the sequence has a U, it is read as RNA, and A pairs with U instead of T. AUGGCUAAC has the reverse complement GUUAGCCAU. A sequence with both T and U gets no answer.
What do letters such as R, Y and N mean?
They are the IUPAC codes for a position that can hold more than one base: R is A or G, Y is C or T, N is any base. Their complements are R–Y, K–M, B–V and D–H; S, W and N are their own complements.
Can I paste a FASTA sequence with numbers and spaces?
Yes. A header line that starts with > is dropped, and spaces, line breaks and position numbers are ignored. Lower-case letters stay lower case, so soft-masked regions keep their case.