About the Reverse Complement Calculator
Reverse Complement Calculator turns a DNA or RNA sequence into its complement, its reverse and its reverse complement. Paste a sequence, as plain letters or in FASTA format, choose whether the answer should use T (DNA) or U (RNA), and the page gives the three results with copy buttons, the sequence length and the GC content. The reverse complement is the sequence of the opposite strand read in the usual 5′ to 3′ direction, which is what you need to design primers, find a gene on the other strand or check a sequencing read. IUPAC ambiguity codes are supported.
Updated October 2026
How to use the Reverse Complement Calculator
- 1Paste your sequence, with or without a FASTA header.
- 2Choose whether to write the answer as DNA or RNA.
- 3Read the reverse complement, complement and reverse.
- 4Press Copy next to the one you need.
- 5Check the length and GC content shown above.
How the strands pair
DNA is a double helix of two antiparallel strands. A always pairs with T (U in RNA) and G always pairs with C. If one strand reads 5′-ATGCCG-3′, the other strand, written from its own 5′ end, reads 5′-CGGCAT-3′. That second sequence is the reverse complement, and it is the one you search for when you want to find a binding site on the opposite strand.
Everyday uses
Researchers and students use reverse complements all the time. Typical jobs are listed below, and each one is a few seconds with this page.
- Designing the reverse primer for a PCR
- Reading a gene that lies on the opposite strand
- Checking a sequencing read that came back reversed
- Finding palindromic restriction sites, which equal their own reverse complement
Tips
Keep the direction in mind. Most tools and databases write sequences 5′ to 3′, and so does this page. If you only want the complement without reversing, use the Complement line, which is written 3′ to 5′ under the original. Always check the first and last few bases against the original to be sure you pasted the right strand.
Related tools
Count the G and C bases with the GC Content Calculator and read the protein with the DNA to Protein Translator. For other letter tricks try the Reverse Text tool and the Binary Translator.
Features
- Reverse complement, complement and reverse
- DNA and RNA output
- FASTA headers, spaces and numbers ignored
- IUPAC codes such as R, Y and N
- Length and GC percentage
- Private: nothing is uploaded
Frequently asked questions
What is the reverse complement?
The sequence of the other strand of a DNA double helix, read in the 5′ to 3′ direction. You get it by swapping each base for its partner (A with T, G with C) and reversing the order.
Why reverse as well as complement?
The two strands of DNA run in opposite directions, so the partner strand read from its 5′ end runs backwards compared with the original.
How do I use it for a reverse primer?
Take the sequence at the 3′ end of the region you want to amplify, write its reverse complement and that is the reverse primer in the usual 5′ to 3′ form.
Does it handle RNA?
Yes. U is read as A's partner and, if you choose RNA output, T is written as U.
What do R, Y and N mean?
They are IUPAC ambiguity codes: R is A or G, Y is C or T, N is any base. Their complements are Y, R and N.
Are lowercase letters and spaces fine?
Yes. The page converts to capitals and removes spaces, line breaks and numbers, such as those in a GenBank record.
Is there a length limit?
No hard limit, but very long sequences, such as whole chromosomes, are better handled by dedicated software.
Is my sequence uploaded?
No. The conversion happens in your browser.