Reverse Complement Tool
Paste a DNA or RNA sequence below. This tool supports standard bases plus IUPAC ambiguity codes (R, Y, S, W, K, M, B, D, H, V, N).
What is a reverse complement?
In molecular biology, nucleic acid strands are read in opposite directions and paired by base-complement rules. For DNA, A pairs with T and C pairs with G. For RNA, A pairs with U and C pairs with G. A reverse complement is created by taking a sequence, reversing its order, and then replacing each base with its complement.
Quick example
Input DNA sequence: ATGC
Reverse sequence: CGTA
Reverse complement: GCAT
How to use this reverse complement calculator
- Paste or type your nucleotide sequence into the sequence box.
- Choose Auto, DNA, or RNA mode.
- Click Calculate Reverse Complement.
- Review sequence stats and copy the reverse complement if needed.
Supported nucleotide symbols
This tool accepts canonical bases and IUPAC ambiguity codes commonly used in primer design and sequence analysis:
- Canonical: A, C, G, T, U
- Ambiguous: R, Y, S, W, K, M, B, D, H, V, N
If invalid characters are present, the calculator reports them so you can quickly clean your sequence.
Why reverse complements matter
1) PCR primer design
Reverse primers are typically reported as reverse complements of the target region. Getting this wrong can prevent primer binding and lead to failed amplification.
2) Sequence alignment and mapping
Reads may align to either strand, so reverse complement conversion is often required during preprocessing or interpretation.
3) Cloning and synthetic biology
Restriction sites, overhangs, and construct orientation checks frequently require quick strand conversion.
DNA vs RNA output mode
The only practical difference in complementing rules is whether A pairs with T (DNA) or U (RNA). Auto mode treats input as RNA if it sees U and no T; otherwise it defaults to DNA. You can always override this behavior manually.
Best practices
- Remove spaces, FASTA headers, and line numbers before analysis.
- Confirm whether your workflow expects DNA or RNA output.
- Double-check strand orientation when designing primers.
- Keep a copy of both the original and transformed sequence for reproducibility.
Final note
This page runs fully in your browser. Your sequences are not uploaded to a server, which makes it convenient for quick checks during routine genomics, PCR, and cloning workflows.