Welcome to CompareTm, a Tm calculator hosted at the Computational Biophysics Group at UFMG, Brazil. Here you will find a simple interface for calculating Tm and compare the results of different parameter sets and conditions. This uses our Linux application VarGibbs. No login or registration is required, simply click on the examples to see how it works. Please email gweberbh@gmail.com if you have any particular need that is not covered here.

We use cookies to remember your last session and store whatever you entered in the form below. We will not pass your data to others and will not use it for any other purpose other than testing. (Disclaimer) This service is provided in the hope that it will be useful to you. To our knowledge this software works correctly and the answers should be accurate within the determined uncertainty. However, we do not guarantee this and we will not be liable for any problems this may cause to you.

(Last modifications: new parameters for single LNA modifications in DNA (05/2023) and new parameters for DNA mismatches (14/09/2023).

If you use the results of this service in your research please be kind enough to cite some of our articles as you see appropriate: for RNA parameter sets of type RNA AOP please cite Ferreira et al. 2019; for DNA/RNA parameter sets of type DNA-RNA AOP please cite Barbosa et al. 2019; otherwise please cite Weber 2015. For citations to parameters from third parties please see here. Thank you.

Click on one of the buttons below to preload examples.
Type or copy sequence here 5'→3': Simply copy your sequence into the box, 5' to 3', you may also add the complementary strand after a slash. Do not worry at all about formatting as any spurious character like spaces or hyphens will be removed. You can use also N in your sequence, this will automatically be replaced by A, C, G and T, resulting in 4 different calculations. For LNA modifications add a plus sign in front of the modified nucleotide, e.g. +A for an LNA modified A.
(optional) Type or copy the complementary strand 3'→5': If you leave this blank, we work out the complementary strand automatically. However, if your sequence contains mismatches you need to fill this in, 3' to 5'. You may also add the complementary strand in the upper box after a slash. Note that we are currently supporting a limited set of mismatches. Click on show available parameter sets (opens new window) to see which parameter sets can handle mismatches.
Type the strand concentration Ct: μM You may enter a list for multiple Ct, e.g. 100,200,400 and we will perform a separate calculation for each. μM is μmol/L in SI.
Select parameter set: Select here the type of sequence (DNA, RNA, DNA-RNA or RNA-DNA) and your preferred set of parameters. Note that only some parameters handle base pairs other than AT (or AU) and CG and that some are available only for limited set of salt concentrations. Click on show available parameter sets (opens new window) to get a detailed description of all parameters available, otherwise just select the first entry to see what happens.
show available parameter sets in new window
(optional) Check to use NN parameters only Check this box if you wish to use only nearest-neighbor (NN) parameters. This will exclude initialization, symmetry and terminal parameters. This is useful for verifying ΔH, ΔS and ΔG that were calculated in this this way. The melting temperatures will not make any sense.
(optional) Salt correction module
Target salt concentration [Na+]: mM You may provide a new salt concentration. We will calculate the salt correction taking as reference the original salt concentration of the parameter set. For example, if you select 150 mM and the AOP-OW04-69, the correction will be from 69 mM to 150 mM. Leave the box empty if you do not wish any salt correction.
Select salt correction: After selecting a target salt concentration please select which type of correction equation should be used.
(alternative 1) Calculate strand concentration Ct for target Tm
Type the target temperature Tm: °C If you provide a target Tm we will calculate what the corresponding strand concentration Ct for the selected parameter set.
(alternative 2) Calculate Tm from ΔH and ΔS
Type total sequence enthalpy ΔHtot: kcal/mol If you provide a target ΔHtot together with a ΔStot, that is, the total enthalpy and entropy variation we will calculate the corresponding Tm from the Van't Hoff equation. This is independent of parameter set.
Type total sequence entropy ΔStot: cal/K.mol
Type the strand concentration Ct(2): μM
Self-complementarity is determined from the sequence above
(alternative 3) Calculate ΔH and ΔS from Tm, ΔG and Ct
Type the target temperature T: °C Provide a target Tm, a target ΔG37 °C and a target Ct, and we will calculate the corresponding ΔHtot and ΔStot. No parameter set is used for this calculation.
Type total Gibbs free energy ΔG37 °C: kcal/mol
Type the strand concentration Ct(3): μM
Self-complementarity is determined from the sequence above
Check to clear previous results